Keep in mind Germany, a major nation with 5 lines has gotten a Swiss sub-tree. This means there is no real reason USSR couldn’t be getting a sub-tree in the future, and Yugoslavia could be a good option.
A bit of history on Goli Otok aka Croatian Alcatraz.
I think YU fits more alongside CZ-SK vehicles.
In 1949, the entire island was officially made into a high-security, top secret prison and labor camp set up by the authorities of the People’s Federal Republic of Yugoslavia,[6] together with the nearby Sveti Grgur island, which held a similar camp for female prisoners. Until 1956, following the Tito–Stalin split and throughout the Informbiro period, it was used to incarcerate political prisoners. These included known and alleged Stalinists, but also other Communist Party of Yugoslavia members or even non-party citizens accused of exhibiting sympathy or leanings towards the Soviet Union.
That said, I don’t think ex-members of YU (excluding maybe Croatia and Slovenia) have anything against USSR or RU as of right now.
Pair that with the fact mixed battles are already happening, especially in higher tiers of air, so we are pretty much used to the “everyone vs everyone” concept.
Already said this in RRD, but I wouldnt have a Yugo sub TT in Russia. Not only were relationships not good (especially after WW2), but many, many Yugo players just want it to be its own tree, as it has enough.
Only times Ive seen them want it there is because they got good amount of the Russian TT grinded
Russia could just get things it had back then, like Belarus
And there is no reason to start worrying if this a sub tree,same thing is going to probably happen to it like with Czeckoslovakia, it won’t be a sub tree