Snip
Detailed response, fun to read! You asked a question about why I said Germany would be in charge (well, what I actually said was more like "nobody would want Germany to be in charge," but your meaning is clear).
My assumptions with a POD around a successful Union Treaty are that it's too late to force the Baltics and possibly some of the Caucasus back into the Soviet bottle, just as it's probably too late to save communism in the Eastern Bloc beyond individual exceptions. The treaty wasn't even proposed until after the Baltics had declared their independence, and also after the democratic reformations of every Eastern Bloc nation.
My assumption is that it's too late for the USSR, reformed or not, to take a leading role in an East European alliance system. Germany was going to re-unify, and East Germany welcomed into the EU. I dwelled for a moment on the possibility that EU expansion might be too contentious with a surviving USSR, but I don't think in Germany's case it would be a problem. After all, if Germany's going to be one again, and it's either going to be in the EU or out of it, better for everyone if it's in. If it were out, it would very likely join any Eastern European alliance that formed, and as the most powerful state in such an alliance, it would dominate- nobody wants that. I hope that clears up why I mentioned Germany.
I guess it's possible a unified Germany might agree to leave ALL alliances and be a big giant neutral, but staying in the EU seems more likely.
But all that hinges upon a POD relating to the New Union Treaty. Were you considering an earlier POD? I still doubt you can keep Eastern Europe on-side without a much earlier kind of POD than one that results in a New Union Treaty. And possibly you can find one that allows for reform with the Baltics retaining communism and some level of peonage to the Soviet Union, but the only way they stay in a reformed USSR is through a lot of bloodshed and likely shipping them all off to Siberia again.