I didn't mean "way too early" as in x amount of years. I meant, "way too early" as in, they're releasing way before the competition, which means that the competition is going to have enough time to make something even better in only about 2-3 years. In fact, it's not an unreasonable assumption that whatever Sony is cooking up right now is already more powerful/advanced than the NX is going to be.
Also, I think it's high time we all realise that gaming generations are lasting longer, and we can't just say "well, they've always been x amount of years long, so they should be/always will be x amount of years long." Things change, including technology, support, games, etc., and that will inevitably affect the generation lifespan.