But making the German kingship de facto hereditary would strengthen the hands of the king vis a vis his subjects, since he doesn't have to fight pretenders or have to fight for his son to succeed in kingship.
But he would have to do that ITTL, even with a stabler dynastic succession, would it be only due to the different geopolitical situation : Capetians benefited from having, if they were relatively weakened themselves, from feudal principalities that neighboured them were as well, if not even more, divided themselves.
Ottonians would have to deal with more unified, more strong and more or less equals in political power when it come to Germany itself, principalities. Contrary to Capetian suzerainty that managed to play on urban freedoms, small lords, suzerainty on vavassor to weaken and won over their immediate rivals; Ottonians would have a more hard time doing so.
Meaning that while Capetian suzerainty became gradually more and more of a present thing, a strong Ottonian suzerainty over strong feudal lords would be more disputed, maybe up to the succession even with a dynastic continuity.
Furthermore, even if Imperial kingship would be distinct, it would be de facto identified as IOTL with a rule over the whole empire, including Germany. Giving that, from its quite particular nature, immediate hereditary succession may have trouble to be adopted for it, its association with Germanic kingship would make it harder to became immediatly hereditary.
Not that you can't end with an hereditary succession, but for these reasons, I think it would be more of a mediatized succesion in a first time, and eventually more regularly contested than in Capetian France, even with a dynastic continuity.
Even if it's likely to end with a continued Ottonian rule, it wouldn't look like a Capetian rule only superficially germanized : it would be something much more adapted to realities (and incidentally, having more chances to last this way).
But would the Pope dare crown another person as emperor who weren't German king yet? Since after 962, I can't think of a single emperor who wasn't German king first.
That's mostly, pointed above, that because being used distinctivly, King of Romans (itself pretty much tied to Imperial kingship : one was Rex Romanorum because claiming the imperium) and King of Germany became de facto a same thing.
That's precisely the problem I was talking above : German kingship became more and more tied up with Imperial kingship, and eventually more dependent of noble and pontifical legitimacy, producing an important number of
anti-kings.
So perhaps a situation would happen were not all kings of Germany would be emperor, but all emperors would be German kings, and if it was de facto hereditary, all would be Ottonians?
It's possible, after all it happened with Henry VII of Germany, but giving the growing identification of German kingship with Imperial kingship, pontifical and noble meddling with Imperial titles would have an important influence over Ottonian legitimacy nevertheless.
And what about the prospect of a king eventually, in the far distant future, just declaring himself emperor elect, like OTL Maximilian,
I don't really see it happening with a classical medieval mindset, where pontifical legitimacy, when tied up to not only Imperial title, but as well Rex Romanorum title is that important.
IOTL, while the pope technically didn't have to intervene on much formal French kingship election, representatives were still often present. You can't just get rid of it too soon : while Capetian hereditary succession was immediate (neither sacre or coronation made the king) you had too much precedent (percevied or historical) with Imperial/Roman titles to get away with.
Maybe a greater distanciation from German kingship and Rex Romanorum/Imperial titles? It's going hard to reach, giving the legitimacy boost it represented : eventually,
no Ottonian HRE may be best for this precise objective.
