Russia is in such a chaotic and lawless state that, really, anything goes. There's no major problem with that idea, and if that's what you want you're free to write an app/sheet. I don't know to what extent a group like that would have control of Siberia, though. In all likelihood, their territory would not make up all or most of Siberia because Siberia is a big place that is not easy to control and administer. There are also likely other groups in the area that would exert their own influence and control so they'd have to deal with that as well. Beyond that, the only concern I feel is worth pointing out is that China [i]will[/i] invade in force at some point. If you want to deal with that, then you're free to stay in Siberia. But fair warning that, when that happens, things will be very difficult for a group such as yours. People on the west side of the Urals are protected by the mountain range, so they aren't as vulnerable to it, but in Siberia you're pretty much right in the way of the eventual Chinese invasion. Again, if you're okay with being an underdog, then there's no problem.

My two cents, but Aaron should also have a say here because Siberia is his side of Russia.