If we for a moment assume that both Microsoft and Sony are aiming at releasing consoles the next generation with the target of being much faster and better than this generation (ie, not the Nintendo reuse strategy) - where would they be in their development process now?
I mean, are they still in the planning stages - everything is still undecided (CPU architecture, gfx hardware)?
Or perhaps they have decided upon the main architecture, and started designing hardware (minor things like RAM amount and clockspeeds still undecided ofcourse).
What can we deduct from previous gen, that is, how far in the planning were the Xbox360 and PS3 back in say 2003 or so?
Earlier than you might realize.
PS2 was being planned in early 1995, before the release of PS1 in the U.S.
PS3 planning was underway in 1999, around the time PS2 was announced and before it was released even in Japan.
original Xbox was being planned (in some form, not as we knew Xbox in 2000-2001) as early as 1998 when Microsoft aquired WebTV and the 3DO Systems team and their MX chipset. Read 'Opening The Xbox'. Actual development of Xbox was going on in 1999.
Dolphin/Gamecube was being planned in early 1998. The IBM CPU already existed in some form. Development of Flipper GPU was going on in 1999.
Wii was being planned / developed by 2000/2001.
Xbox 360 planning was underway in early 2002.
'Read The Xbox 360 Uncloaked'
by 2003, Xbox 360 and PS3 were far beyond planning, well into actual development. Xbox 360 was completed by late 2004. PS3 completed in 2005.
PS4 was being planned as early as 2005, since both Sony and Nvidia talked about future plans then. Sonyand Nvidia had a roadmap for graphics that started with RSX. No doubt it extended to PSP2 and all the way out to PS4 (at least on paper).
Xbox 3.0 was in planning by 2006 with the reports about Microsoft developing its own CPU.
By now I expect Xbox 3.0 and PS4 to be far into planning, and perhaps into actual early development. They're more than 2 years from release. The soonest release for Xbox 3.0 that's even within the realm of possibility would be late 2010. that's just over 2.5 years. I think late 2011 is a much more likely possibility though, so that's a little over 3.5 years.
I'm sure Nintendo was working on Wii 2 stuff before the Wii came out, and I imagine it's in development now. I wouldn't be surprised by a 2010 release, but most likely 2011. They've been releasing new consoles every 5 years in the U.S. since the SNES (1991, 1996, 2001, 2006).
Console companies almost always start some sort of work on the next generation BEFORE the new current generation system is released.