Is Sarajevo as capital of Tito's Jugoslavia at all likely? It would stay truer to the state line of a south Slavic paradise, instead of suggesting (and acting like) 'Big Serbia'.
It's likely, and is actually in quite the central location, but it has some major flaws:
- It's in the middle of nowhere - the geography of the region makes it expensive to connect it to the rest of the country. I shudder to think what the roads would be like there if it were not for them winter olympics. It's most natural connection is via the Bosna river valley, which flows into the Sava, the longest tributary of the Danube, that joins the Danube at... Belgrade. The second easiest alternative is the Drina, but it's basically a gargantuan canyon until Loznica.
- Rather limited space to expand, being in a narrow valley - this also causes nasty pollution problems in winter
- Belgrade is simply the best possible location for the capital - on a massive junction, with easy access to all natural paths to any point in the country, with the exception of the littoral which has a rocky wasteland sort of terrain so it is basically forever isolated. Also, a very central location if Bulgaria gets integrated
- Would, paradoxically, require that during WW2 that basically the entire OTL communist party die and be replaced by others - Tito and his cronies were actually rather unsavory characters (like basically having a good deal of the former Ustashe later placed in major party roles), and the entire country was basically set up for collapse from the idiotic internal borders from the start. Belgrade was kept as capital to make the others think that the Serbians are the favored people (and are a plurality anyway), but the internal borders were specifically drawn so that when a state eventually rebels, a significant Serb minority absolutely refuses to join and counter-secedes instead, as of OTL. OTL SFRY was basically the most antiserbian Yugoslavia possible, where everyone got screwed in the end, but Serbs most disproportionally
Let's see for some, the geographically best possible locations
China: I see Shanghai or Nanjing (or anything between, on the river) as excellent capitals - natural entry points into the country that allow the most complete access.
Russia: A bit south of Kazan, the confluence of the Kama and Volga rivers - allows for increased control over Siberia and Central Asia. If many things go as OTL, it also means that Russia is even harder to subjugate from the west than OTL.
Yugoslavia: apart from Belgrade, maybe the site of Rača on the confluence of the Sava and Drina could serve well. It's basically the meeting point of Serbia, Bosnia and Croatia (despite the fact that the area is basically Serbian thoroughly)/ The biggest drawback that it isn't on the Danube and therefore less shipping passes through (but it's also slightly more shielded from invasion from the north due to Fruška gora). Another drawback is slightly increased distance to the Morava valley, probably the most important land route in Europe since it connects basically everyone with Asia.
(greater) Romania: I see the village of Patlagancea north of Tulcea as Romania's answer to Egypt's Cairo - the place where a river delta starts is always very suitable for a city. Also allows easy access to both Wallachia and Moldavia. Not to Transylvania, but Romania's geographic setup basically mandates that no matter where you put the capital, Transylvania will always be a little more cut off. Except if you put the capital in Transylvania. Then everything else is cut off.
(northern) Macedonia: Stobi. Central location, has a natural path to Pelagonia and really everywhere else. An ancient city used to be there, so it helps with their LARP thing they have. Also not full of Turks and Albanians, so the politics of the place are a little more relaxed than what is happening now.
Turkey: Istanbul. Any possible drawback is massively negated by it's eternal significance
France: either at the mouth of the Seine, Nantes, the confluence of the Garonne and Dordogne rivers, Arles (place where the Rhone delta starts). Problem: demands an absolute behemoth of a POD due to the fact that each and every single one were held by foreigners and therefore prevented from becoming the major economic centers they have the geographic potential to be. In a more land-based France, then Orelans or Bourges is absolutely perfect, and more plausible.
Big Germany/Big Netherlands/HRE on roids/surviving Frankish Empire - the start of the Rhine delta. The entire area is ludicrously densely populated OTL for a good reason.
Germany as-is: Hamburg, Bremen, Mainz, Gottingen
Greater Croatia: as much as it is very ironic and at the same time rather grotesque, but Jasenovac, due to the fact that it would provide rather easy access to any point. Also might be the center of potential population (since we know what the Ustashe were like, it would definitely not be the center of population)
basically any Mesopotamian state that doesn't end up having the Arab river as the border (basically 100% of the cases, OTL was some sort of unholy fluke): Basra.
big Congo/surviving Kongo state: Boma.
Nigeria: Lokoja, or starting point of the Niger delta,
USA: either New Orleans, or Cairo. Both allow much greater control over the entire country (and would help with having the "flyovers" have more population)