2 years minimum which is actually good news for gamers as they are forced to refine existing game engines & squeeze a little more out & the consoles are getting cheaper gradually as the volume is increasing & they become more mainstream.
Also the next gen will most likely be 32 bit so restricted to 3.5-4Gb System Ram max I doubt they will bother with the extra complexity of 64 bit software anytime soon.
I would expect 2Gb Vram minimum & perhaps be modular to allow for future expansion like a new CPU/GPU etc etc
Erm lol, extra complexity of 64bit.
They've had years of practice on the x64 platform.
Look at the fuss they made over the CELL in the PS3.
They're not worried about making it hard for developers, they need to move on.