Nostalgia is definitely a driving factor, but I'd put money on a demographic of gamers that are frustrated of 'pay to play' games and constant downloads and updates.
This is a simple console with a proven track record, and simplifies the gaming process. Since millennials are all about the new wave of 'hipsterism', the Nintendo Classic targets three demographics:
- Gen X and Y'ers with a case of nostalgia.
Frustrated gamers that want a simpler gaming model.
Millennials who will find it 'hip' to own one.
... enough to make a f##kton of money, in other words.