Regarding Otto's hegemony in the West Frankish kingdom (specifically, after 946, because he doesn't have one before that), I think we're disagreeing in quantative not qualitative terms. Otto _can_ intervene, he _does_ intervene, but his goal is a peaceful West Frankish kingdom which doesn't try and claim Lotharingia. This is still a major potential threat - Louis was an active presence in Lotharingia up until at least 942 or so, and his efforts in 939 were by no means a fiasco. There is a case to be made that it's only Otto's excellent luck in having the two main leaders of the rebellion against him die in one battle that year which stops him from getting kicked out of Lotharingia the same way Conrad did in 911. (Now how's _that_ for a PoD for a revitalised West Frankish Carolingian dynasty!)
As for the potential brides, we might add two more:
- Emma, daughter of Hugh the Great, in OTL wife of Richard the Fearless of Normandy (depending on which one of HtG's wives she's the daughter of - it's unlikely Lothar would marry his cousin!).
- Adele, daughter of Robert of Troyes, in OTL wife of Geoffrey Grisegonelle of Anjou.
Ranking our six choices in order of probability, Adelaide-Blanche is at the bottom. You're still overestimating the importance of the Angevins - in Brittany, for instance, Fulk is unquestionably the junior partner. He's present, sure, but it's Theobald to whom Alan Barbetorte (supposedly) commends the province on his deathbed, with Fulk only brought in later; and all the surviving charter evidence indicates that Theobald was pre-eminent over Fulk in Brittany (he always signs first, for instance).(1) That the Angevins play a secondary role in royal politics is even more true in the Aquitanian marriage. First, there's no reason to think Richer is wrong in ascribing Aquitanian motives for the marriage. Sure, there might be well-entrenched families in Poitou and Tolouse, but the Auvergne and to an extent the Limousin - i.e., where Lothar tries to embed Louis - don't have much in the way of central authority, and of course the reason to wed Louis to Adelaide in the first place is to wrest real control _back_ into the hands of the monarchy! Again, they're married in Brioude and the marriage falls apart when it becomes clear that Adelaide can't give Louis command of the region (2); in addition, another chronicler (Ralph Glaber) refers to her specifically as 'the Aquitanian woman'.
On the flip side, postulating an anti-Robertian motive for the early 980s doesn't make a lot of sense. Theobald is dead, but his son Odo I has all his father's lands and maybe more, as well as one of the century's tighest alliances with Heribert the Elder. Geoffrey Grisegonelle is probably more powerful than Fulk the Good, but he's not more powerful than the Thibaudines, and the big leap forward there doesn't come until the reign of Fulk Nerra. Whereas in c.980, Geoffrey is count of Anjou and _maybe_ of Chalon-sur-Saone and a well-regarded warrior, Odo I is ruler of Tours, Blois, Chartres, Chinon, Chateaudun, as well as a big chunk of lands east of the Seine (whether or not he's got his uncle Heribert's lands at this point is up for debate, but he's definitely got his mother's). Given this, Lothar already has an alliance with the kingdom's most powerful noble. Which raises another point: by this point, Hugh Capet is already - well, neutered is a bit strong, but he's not exactly bestriding the kingdom like a colossus the way Hugh the Great was. Case in point: after he submitted to Otto II in Rome in 981, most of the old Loire valley _fideles_ seem to have deserted him. Gerbert of Rheims' line about Hugh being the real ruler is pure bombast - after about 980, he was not an insignificant figure, still a first-rank noble, but not a terrifying, greater-than-the-king presence; and Lothar's primary concerns are first his Aquitanian gambit and then, and more importantly, Lotharingia. (And, arguably, they have been since he successfully broke up and weakened Hugh's inheritance in 956-960.)
All this leaves, then, is a low-status girl who is a daughter of a second-rate vassal and who doesn't bring any particularly useful connections. Not the most appealing prospect in our brideshow!
The second-least probable... probably Emma daughter of Hugh the Great, partly because there are questions of incest but also because I don't think either Hugh or Louis are going to want it... too much bad blood.
Ditto for Emma of Blois, who comes next. I think you're absolutely right that Louis seems (understandably) to have kept a grudge against Theobald, and this will probably feed into any marriage prospects.
Next is Adelaide of Aquitaine. Adelaide might actually be a pretty good choice - high-status, roughly the right age, renews the Poitievin alliance which Louis put together in 942. A solid possibility.
Second is Adele of Troyes. TBH, Adele and Adelaide of Aquitaine could well go either way; there's not a lot to choose between them. Adele's big advantage are her links to Burgundy. Her father, Robert of Troyes, married one of the daughters of Gilbert of Burgundy, and seems to have been close to Gilbert. He and Lothar were briefly allied against Hugh Capet and Otto of Burgundy in OTL anyway - a marriage between the two families might really bolster Louis' position in Burgundy, which is important because for most of the mid-century the Carolingians seem to have been a lot more interested in ducal Burgundy than the west of the kingdom. The major minus point is status - Adele is a suitable bride for Geoffrey, but is that really suitable for Lothar? There's also the fact that Adele's grandfather shut Lothar's up in prison until he died - there _may_ be a grudge there.
Still, Emma of Italy remains the most probable choice: she's a closer link to the Ottonian court, which Queen Gerberga and probably Archbishop Artald of Rheims will be urging; she's not incestuous, and she's very, very high-status. There just aren't that many princesses around who m Lothar can marry without breaking incest regulations, and the Carolingians, Ottonians and early Capetians do seem to have preferred marrying these high-status women where possible, even if they had to import them from quite far away (3).
This doesn't necessarily have any bearing on the family's biological chances for survival. This is a low-fertility, high-mortality time. The Carolingians, c. 980 or so, were doing pretty well biologically: three mature adult males, two married to fertile females. Given how chancey sexual reproduction is, it's best to think of marriages like the stock market: past performance is no guarantee of future heirs. Emma already had either two or three children (I don't think there's any reason to put Richard as illegitimate); she might get another, or the ATL siblings might survive. It might be that thinking about the marriage politics is overthinking it: Louis V's death would be a very easy thing to butterfly away.
In any case, the prospects for Carolingian resurgence are one thing - the dynasty was indeed in the midst of some good times when they were snuffed out OTL, but what intrigues me is getting them higher, faster...
Hence, indeed, Lotharingia 939. If we swap the bad luck around, so that Gislebert and Eberhard live and Hugh the Great dies by accident, then we have a situation in which the kingdom's most powerful block of _honores_ has, at best, one newborn baby as heir, and at worst is up for grabs. I reckon that Louis can entrench himself in not only his royal heartlands but also in the Paris basin and Robertian Burgundy by the mid-940s; in any case, as the man whose sanction is the best legitimising mechanism available, his court now has a _lot_ more pull. In addition, Louis is still the nominal leader of a very menacing rebellion in Lotharingia against an Otto who is not at this point 'the Great', but a newbie king who's doing a good but not great job of managing the inevitable succession disputes. Lots of problems, but also a lot of possibilities...
(Whew, that went on longer than I'd intended!)
(1) Translating the _Chronicle of Nantes_, which is the only narrative source for Breton history of this period, cap. 36: 'Duke Alan, becoming gravely ill, commanded Theobald, count of Blois, that he should come to visit him [...] When the prelates and magnates [of all Brittany] were gathered in his presence, he commanded that they should give fealty to his little son Drogo [...] and his brother-in-law Theobald, his son's uncle, to whom he committed all his goods and his son...'
(2) As for taking Richer at his word, it's from Richer that the idea that Louis behaves 'frivilously' comes. Even if we are inclined to believe him, though, he foregrounds the problem as being that 'the royal title did not avail them enought to allow them to exercise any of the prerogatives of kingship over the magnates of the region', and the marriage only ends when Lothar calls Louis back, and he only does that because his kingship has failed.
(3) A quick and dirty list (not counting those who were married and fell into the throne unexpectedly, so not Hugh Capet and not Henry II):
CAROLINGIANS
------------
Louis IV: Gerberga, daughter of King Henry of Germany
Lothar: Emma, daughter of King Lothar of Italy
Louis V: ...is the exception here, largely because of the political concerns about Aquitaine outlined above.
EARLY CAPETIANS
---------------
Robert the Pious: (1) Suzannah-Rozala, daughter of Berengar II of Italy; (2) Bertha, daughter of Conrad of Burgundy; (3) Constance, daughter of William of Arles (maybe adding a point to Adelaide of Aquitaine above, but by that point in Robert's life he was running up hard against incest regs).
Henry I: betrothed to the daughter of Conrad II of Germany, married to (1) Matilda, ancestry uncertain but non-royal; (2) Anne of Kiev, daughter of Yaroslav the Wise
OTTONIANS
---------
Otto I: (1) Edith, daughter of Edward the Elder, (2) Adelaide, daughter of Rudolf II of Burgundy
Otto II: (2) Theophanu, (probably) neice of John Tzmikes, Emperor of Byzantium
Overall, not _quite_ universal, but a very strong preference not to marry down the status ladder.