Whenever they can cram some 8-10x more juice in reasonably priced console.

I think a decade for one generation is absolutely ok. Especially today with all that computing power in the consoles. I know there are people that aren't happy with the power of PS4 and Xbox One, but I personally can still play with PS3 graphics. It's just good enough at some point. Anyone who needs dat 4K or whatnot can get himself a decent PC and enjoy the grfxxx at anytime without waiting for some kind of new generation. But I don't see why there should be new console hardware around every few years. We're not talking about iPhones here, it's still the software that counts in gaming.

Mix of

a) new technology is ready, that ll make new experiances possible, or better experiances than current tech does.

b) price of new tech is affordable.

c) hardware sales have stagnated & software sales have declinded.

Just baseing it on hardware sales alone, is not a good idea.

Stuff like new proccess nodes matters alot in this.

In the future of consoles (PS2 & Xbox Two), stuff like 3D stacked memory & 3D stacked chips, will be all the rage.

Once a tech like that becomes availible that trumphs the older stuff by a huge factor, its time for a new gen.

**edit:

If nintendo would man up and not hold back.

I would like to see them use the newest process nodes availible to them.

I would like to see a  16nm FinFET  APU with hybrid memory cube technology, that for a cheaper price than a PS4, makes the PS4 look slow.

Them launching "late" with the NX to compete against the PS4 & Xbox One, make it a possiblity.

Since they wont have launched their competeing product until 2016/2017.

I wish they would do that, and at the same time Im sure nintendo wont. >_>' they make really weird hardware design choices.

I think nintendo is so closed in their own world they can`t see what is in front of them. Back in the day of NES and SNES they had 3rd party support just because they were the biggest system and there was no where to go. With PS1 being super 3rd party friendly, with CD and lower royalties, they all jumped the PS1 bandwagon. This is not a Nintendo thread, but they should just be rushing their new console ASAP, Wii U is beyond salvation. I hope they get a good hardware, I don`t even understand why didn`t want to compete with PS4 and X1, it`s not like they have the ultra advanced specs PS3 and X360 had for their time.

Probably fans that don't like being in second or third place lol. I'm glad the seventh gen went as long as it did. 

Then it's up to the company to make a comeback. The ps3 and 3ds show it's possible

when there is a money there is a reason lol