I just started a huge thread about a Greater Yugoslavia following WWII so if anyone is interested take a look at that. here's the link:
https://www.alternatehistory.com/discussion/showthread.php?t=231249
I think that if Tito had offered to make Macedonia an autonomous province of Bulgaria on the condition that Bulgaria join Yugoslavia as one of its republics (as opposed to an equal partner) the Bulgarian leadership may conceded to such a trade off and joined the Yugoslav federation. Bulgaria entered WWII with the goal of finally annexing Macedonia and creating the Greater Bulgarian state it for decades fought for. If Tito made such an offer it would be difficult for the Bulgarian leadership to reject it. Sure, one could make the claim that Bulgaria would probably never agree to voluntarily give up its sovereignty and cede leadership, however, Bulgaria had already de-facto lost its sovereignty following the Soviet victory and was about to lose it anyway along with all theo ther countries of Eastern Europe. By joining Yugoslavia, Bulgaria would be able to achieve its war aims and annex Macedonia, and although it would lose its sovereignty, it would also never become dominated by the Soviet Union following Tito's split with Stalin (which of course occured later).
Now a Yugoslavia that included Bulgaria would undoubtedly help calm fears of Serbian domination and balance out the various national groups. I think that it was stupid and there was really no need for Tito to create artificial 'macedonian' 'montenegrin' and 'bosnian muslim' nations as a way of solving Yugoslavia's national problem. In fact, including Bulgaria in Yugoslavia would have eliminated the need to create a 'macedonian' natioanlity at all, since most macedonians were either Serbs or Bulgars before WWII (i'd say around 75% were Bulgarian while 25% Serb). Both Montenegrin and Bosnian Muslim nationalities are completely artifical and unncessary.
Yugoslavia would then be a federal state consisting of four republics: Serbia, Bulgaria, Croatia, and Slovenia. The constituent nations of Yugoslavia would be Serbs, Croats, Bulgars, and Slovenes. Each of the four republics however would have autonomous provinces in areas that either had significant minorities living in them or had a historic tradition of independence and regional self-identification. As has already been mentioned, Macedonia would have been an autonomous province of Bulgaria, and I also think that Rumelia could have created as an autonomous province in order to integrate the large Turkish minority in Southern Bulgaria and also reduce the dominance of Bulgaria in the federation.
I think that Serbs as the largest nation and traditionally the leaders in South Slav unification, and also their clear victory in WWII unlike Bulgarians, Croatians and Slovenians who sided with the Axis, makes for a strong case for why the capital of Yugoslavia should have still remained in Belgrade. The autonomous provinces of Serbia I believe would be Vojvodina in the North for Hungarians. Instead of making Montenegro a republic (which was pretty useless on the side of Tito, since the country barely has 600,000 inhabitants) it should have been created as an autonomous province within Serbia. However its territory should have been expanded to include all of Sandzak (novi pazar and whatnot) along with all of Kosovo. I think this would have been a much better call than to create only Kosovo as an autonomos province within Serbia. By making Montenengro very huge it would have reduced the dominance of Albanians in the province and discouraged separatism.
I also believe that Bosnia-HErzegovina should have been attached to Serbia as an autonomous province to which the Peljasac Peninsula (Dubrovnik) would be added as the Herzegovinan coast. This is because Serbs clearly formed a majority in the province before the massive slaughter of Ustashe during WWII and also because Bosnia's muslims would be forced to declare themselves as either Muslim Serbs or Muslim Croats, the majority of which I think would opt for a Serbian identity. I'd say out of Bosnia's Muslims 75% would consider themselves Serbs while 25% would consider themselves Croats. This would give Serbs a clear majority in Bosnia, and satisfy Serbian desires to have more Serbs live together in their own republic. I think that adding the Mljet republic area around Dubrovnik to Bosnia would also have been necessary to give Serbia a much needed coastline, although it would still remain relatively small
Finally in terms of Croatia, I would make Dalmatia an autonomous province, since Dalmatians even today have a strong sense of regional identity and historically have long been seperated from their Croatian counterparts in Hungary. I would also hvae made Istria an autonomous province, however in my opinion, it would have been better to make it an autonomous province of Slovenia isntead of Croatia. This is because it would give Slovenia access to the sea and a coastline, something which all the republics would then have. It would also incorporate the large Italian minority in the area. I also think Trst should have been given to Yugosalvia following wWII and not Italy, so Trst would be made the capital of Istria
So basically here's what a better Yugoslavia would have looked like: Four republics and seven autonomous provinces listed below
1. Slovenia
-Istria
2. Croatia
-Dalmatia
3. Serbia
-Vojvodina
-Bosnia
-Montenegro
4. Bulgaria
-Macedonia
-Rumelia