What makes this a special case is that on the one hand these weren't really immigrants, but rather folks who moved to a different part of their own country and suddenly found themselves screwed over when the borders changed. On the other hand they are also the settlers from the former imperial power, a category which does not tend to fare all that well following decolonization.  So this isn't really like the Kosovo situation where you had a region with a longstanding bi-national population where the local majority sought to gain independence from the ethno-state of the local minority and initially the minority imposed a highly repressive and discriminatory rule, and then when the majority won a bloody civil war, it proceeded to ethnically cleanse a large chunk of the minority population.

However, I don't see how the EU can fairly act unless it imposes a uniform obligation of citizenship by birth and a ban on using any language or cultural criteria in the naturalization process.

NB Anybody know how the proporations of citizens/stateless/Russian citizens have changed, if it all over the past fifteen years?