It is really hard to decide which hardware should be used for a Linux based console. Basically the Nvidia runs everything rule is already broken by Killing Floor. I tried to report the bug to icculus and via the tripwire contact form but nobody contacted me. I compared fglrx vs. nvidia (and after i packaged mesa 9.1 intel as well). That game checks for nvidia vendor and enables some stupid hack that show rendering errors with OpenGL on Win too - they only work in Direct3D mode. If you use apitrace and record the opengl commands then you can playback a recorded session with fglrx cards flawlessly with nvidia driver - when you try it the other way then you see the rendering errors with fglrx as well.
Basically nvidia 310+ drivers have been tuned a bit for the new steam games. Mainly tested with source engine games like TF2 and Serious Sam 3. Nvidia 304 drivers are much slower especially when you don't force performance mode (cpufreq). fglrx still has got more issues with that - especially with slower cpus (or just say: amd cpus in ondemand mode). Valve could use a wrapper that changes cpu to performance mode when a game is started, maybe in general or just for more demanding games.
So when you look at the next option it would be intel only. Haswell might faster than HD 4000 (could not test that) but Intel driver in general is really bad supported by Serious Sam 3. With a hack and gfx to lowest it runs but it looks extremely ugly.
Killing Floor on Intel is not really fast but you could play it. TF2 was ok, similar to cheaper nvidia gpus.
So what did i do? I exchanged my gfx cards depending on the game i wanted to play... That can not be the solution for a console. It does not really matter which gfx solution will be used for valve's own source games (fglrx is right now only problematic with AA enabled, but i hope amd can sort this out) but for 3rd party games it looks different.
If you really combine a i5 cpu with nvidia dedicated chip then you can not call the result a console, thats just a normal gamer pc. A modified PS4 gpu without sony extra commands maybe with fewer cores but higher clockspeed might be an interesting option but it depends on amd at what speed such a chip could run (and what cooling is needed). Currently amd has interesting gfx options, but intel has the better production process. So maybe let intel produce the new amd apus that they could run at higher clockspeeds. You have to see that when sony wants an 8 core system (basically 8 integer and 4 float cores) the clockspeed will be just adjusted so that the power use does not raise over a certain level. But that resulting speed is most likely too slow for current Linux ports. The Win counterparts run much better, some because of more optimizations in the engines like the Unreal 2.5+ based Killing Floor game or Serious Sam 3, the other problematic thing is the default Linux sheduler. It switches so often tasks when another core is unused but downclocked that it can not scale up fast enough. Games like SS3 suffered from that and they tried to bind the main logic to always the same core. The speed is still not optimal for other games.
It dont see a Steambox winning against PS4 even if would be similar priced (unlikely as PS4 will be sold much more often). It is somehow always a matter of time, but right now the time is not working for Valve because PS4 will hit the stores for xmas. I don't think that ppl will buy a 2nd console thats just a pc in a different (smaller) case to play less optimized games. In case it would really be intel cpu + nvidia gpu combined it would be VERY expensive, intel only would too slow for some games (even with haswell), default amd apus you can completely forget, that ps4 thing maybe. When you need to combine a cpu with ddr3 and a 2nd chip with gddr5 it will be more expensive as well, maybe a tiny bit cheaper than intel but it will use more power.
What should happen is that important 3rd party game devs get help from amd/nvidia/intel to really optimize the opengl codepath. That this can work you can see with the source engine - nothing is more frustrating than a game that runs too slow on Linux and on Win it runs great on the same hardware. Not every game is so demanding but some really need more speed. I don't see the problem only in the driver quality - when you compare SS3 Direct3D vs OpenGL then OpenGL is just slower - no matter if the OS is Linux or Win or if you use Fglrx or Nvidia or Intel gpu.