Beautiful map.
Certainly much more likely to guarantee peace than the OTL treaty, if nothing else because Bulgaria, Hungary, Germany, and Italy seem less pissed, the Hashemites seem to be getting what they've been promised, and a lot of disputes are prevented, but I do see a few major points of tension and some interesting things.
1) West Ukraine. Even if somehow the Russians don't have aspirations on it, it will definitely be supportive of liberating its eastern brethren from Russian rule, and if nothing else will be a hub for eastern Ukrainian separatists (which in turn will make Russia view it as a threat)
2) The Turks are obviously very unhappy
3) GigaSerbia. Minus the fact that it lacks Montenegro, it seems to be built around the territory where the Shtokavian dialect/language is spoken (I'm honestly really tempted to argue that standard Croatian which is part of Shtokavian Serbocroatian is a separate language from Kajkavian, especially spoken Kajkavian, which I would say is a transitional dialect of Slovenian). While that is somewhat coherent, there is already a well developed, unified Croatian national identity encompassing Croatia, Slavonia, and Dalmatia. Now, there are many Serbs in Slavonia at this point, but Southern Dalmatia may prove troublesome for the Serbs, even with such things as the "catholic Serb" movement in Dubrovnik and Serbian rule of the region south of the river Cetina in the middle ages, most of southern Dalmatia and a less overwhelming majority of Slavonia is inhabited by Catholics, practically all of whom are, and identify as, Croats, and not Serbs. Croatia is likely to want them, many of them may want to be part of Croatia. Now of course, Croatia-Slovenia alone probably can't retake them from Serbia which I expect to militarily far outclass it and be internationally somewhat well connected as far as allies go, but if Croatia can find some friends, it may be confident enough to go for those lands. Also, like IOTL, Serbian attempts to assimilate or at least de-Croatize those regions will breed resentment. Croats in western Herzegovina may be similarly troublesome. I know it's based on the treaty of London though and barring the creation of Yugoslavia, Serbia would certainly push for this.
4) Independent Montenegro is interesting. I wonder how you intend to maintain its independence. While some Montenegrin politicians today like to make a big deal out of the Serbian annexation, at the time it was quite popular (not only that but it was requested by the elected government).
The ruling coalition was headed by a party whose overt platform was the deposition of the house of Petrović-Njegoš and unification with Serbia under the house of Karađorđević. Now, this particular stance was not necessarily held by the majority (albeit a sizable minority wanted exactly this), but unification with Serbia was overwhelmingly popular.
Keep in mind, unlike Croatia and Slovenia which had distinct and well-established national identities, Macedonia which saw itself as Bulgarian at the time, and Bosnia where the Bosniaks had a different religion and, though still building their identity, had already developed some tension with the Serbs, Orthodox Christian Serbian/Serbocroaian-speaking inhabitants of Montenegro in 1918 would have seen themselves as Serbs. Even the king himself identified as such and wrote Serbian nationalist songs where he referred to the Serbian emperor as "my emperor" and spoke of longing for the monuments of the medieval Serbian kingdom and empire in Kosovo. Hell, on the topic of the king, Nikola had in private letters seemed to view unification with Serbia favorably, but, given his actions after the annexation, evidently expected a setup where he retained some kind of power, perhaps like how the German empire kept the kings of other states in power as subnational monarchs.
The Montenegrin ethnic identity would only really arise in response to poor Yugoslav rule and would remain quite fringe, with most Montenegrins even after WWII identifying as Montenegrin but seeing that as a subset of Serb. Even today most Montenegrins, including a huge chunk of those who do not identify as Serbs, would say that they speak the Serbian language and, if they are religious, that they belong to the Serbian Orthodox Church. Even early anti-Serbian figures like the fascist collaborator Sekula Drljić romanticized Prince-Bishop Petar II of Montenegro, an unabashed Serb patriot and romantic nationalist (which modern Montenegrin identitarians do not, precisely because of his inseparability from the Serb identity), showing just how nascent Montenegrin ethnic separatism was. Again, practically throughout the 20th century, Montenegrin ethnic separatism was fringe. Not Montenegrin political separatism/autonomism. While those who opposed unification were a minority, even among them, many, perhaps even most, saw themselves as Serbs, just ones with a separate country (somewhat like how Austrians are still German, just not part of Germany).
Now, independent interwar Montenegro can be a compelling narrative, but it is in a precarious position where even much of its own population does not support its independence (and foreign backing would only give the pro-Serbian side and Serbia itself more credence as it gives them the option of rhetoric claiming that Montenegro is under foreign rule and forcibly being kept separate from its Serbian brethren). Could be very dramatic, and a more distinct Montenegrin identity could develop (as it did IOTL), it's just not really there yet, and that will cause tension and drama.
5) I hope Italy doesn't stay in Georgia for too long.
