That's the funny thing, though: although the language groups are Estonian vs Baltic, Estonia and Latvia have to a very considerable extent had the same history, and Lithuania a differant one altogether. This is still visible today, when Lithuania has a much smaller Russian community and treats it much better, whereas Latvia and Estonia have both followed the "ethnic democracy" road.
Going back before the Russian Revolution, Lithuania was Catholic with Polish landowners, and Estonia-Latvia was Lutheran with German landowners. And of course in the post-revolutionary period, Lithuania was often something of a pawn to the Soviets in foreign relations, which hardly endeared it to its neighbours. It's only since the events of 1941-1991 brought them toegether that all three Baltics have felt a sense of togetherness, really.
I don't find the scenario at all likely, but Goldstein's idea is the best. Kaliningrad is pretty much out bar World War III, because that's where Russia keeps a disproportionate number of its military assets. Any local oligrach with pretensions to being the ruler of his Fourth Baltic Republic is likely to be unseated by the Russian troops.