This will last at most only 5-10 years more [1]. Poland, Romania, Bulgaria, Italy, Spain and Greece are brain-drained to the bone already. There is noone to come over.
I met a lot of brilliant people from all over the world during my undergrad at TU Munich; many of them stayed. Google, Apple, Microsoft have expanded rather aggressively over the past years, and the startup scene is growing. Berlin, Hamburg, Frankfurt seem to follow suit.
Granted, it's much less likely (and also less politically incentivized) to become a "millionaire employee", but I guess ultimately, the correlation between wealth and wellbeing is simply weaker in (northern) European economies? As long as immigration policies don't change (and why would they? the current model aligns well with lobby incentives), I don't see much reason for this to change.
Also, Poland, Romania, Bulgaria, Spain, and Greece have a different political and economic history than Germany, France, Denmark, Sweden, etc.
I don't know how what the retirement scheme is implemented over there, but if it is generational (young gens pays for older gens) they willy have a BIG problem in 15/20 years ...