> Some of those movements are in areas landlocked or not economically viable, but the Free Ingria movement (Leningrad oblast, including St. Petersburg) has potential. That area is bordered by Finland, Estonia, and the Gulf of Finland. An independence movement there could be well supported from Europe.
Most successful independence movements are based on some kind of distinct ethnic/national/cultural/religious/linguistic identity. “Ingria” is a historical term, coming from a time several hundred years ago when the area was ruled by Sweden and populated mainly by Finnic and Baltic peoples. However, the vast majority of its current population is ethnic Russian, and the Finns and Balts are now only small, highly assimilated minorities. The vast majority of its population don’t identify as “Ingrian”. That does not seem like a successful basis for an independence movement.
I think the most likely place for renewed separatism is Chechnya. Not right now while Kadyrov and Putin are so close, but if something happened to one (or both) of them, or if they had a falling out, it could easily start again. And spread to Dagestan, Ingushetia too, maybe even the entirety of Russia’s North Caucus region-in most of which ethnic Russians are a minority. An Islamic separatist movement is likely to find international support and funding from the Islamic world.