Your challenge, should you choose to accept it, is to have the Soviet Union democratize, but remain as one country. No POD limit, but the USSR's democratization has to occur around a roughly similar timeframe as OTL, and it has to be at least as democratic as OTL's post-Soviet Russia (which, I admit, is setting the bar kind of low).
I was curious enough about this to add up the ex-Soviet countries' population and GDPs (using wiki data)-together, they have a population of around 289 million and a GPD (PPP) of $3.43 trillion, and would, if united, be the world's fourth largest country by population and its fifth largest economy. (I expect that, had they actually stayed united, both those numbers-especially the GDP-would be larger since some republics might have avoided OTL conflicts and other economic disruptions)
Further thoughts?