I like 5 to 6 year gens, with notable support continuing for at least another year. That's long enough so that early adopters can enjoy having a relevant product for over half a decade, but short enough so that the tech doesn't ever become ancient enough to limit software. In my mind, 7 or 8 years leads to a great library of games for a single console, but you either end up with laughably outdated tech by the end (see the Game Boy minus Pokemon) or you have a very expensive beginning of the generation (see the PS360).
Of course, this is based on the assumption that my game consoles will play older games too (based on my experience with the Game Boy series, PS2, Wii, and Wii U), so the new policy of removing backwards compatibility may change my mind about short generations.







