It would take a lot of engineering to be successful with this, but it would still be possible to have upgradeable consoles where developers wouldn't have to make any specific configuration considerations (to some extent). If you based your GPU off of a processors in the Radeon 58xx line of graphics cards, told developers that the native resolution of games would be handled by the system (not their software), you could have 1 GPU render at 720p with 4xAA, 2 GPUs render at 1280x1080 with 8xAA, and 3 GPUs render at 1080p with 16xAA (or whatever).

In ways it is an appropriate approach because it allows users who don't (really) care about 1080p to get their system in an affordable package, while those who do care and are willing to pay for it can also get 1080p.

Sounds like music to my ears.

They really would only need single or double GPU configurations. And it could just be an add on. Video card in a box which you slide in, much like a hard drive, enabling crossfire/SLI. And it gives the console more juice to push pixels on the hardware level. 

They can addres the power issues with separate adapter (double 6 pin lol) and could squeeze more money out of willing consumers for hardware and wouldn't need to lose money at launch.

I like the idea, but they could use it expand the life of the console. Say, just as an example, that you launch your console 1 or 2 years earlier than your competitors that has X graphics power but with an overpowered CPU. You get an install base, developers work using your hardware and after those 2 years the others launch their consoles that are twice as powerful as yours. What to do? Just announce the add-on that doubles your console's graphics power and puts it at the same level as the others, but with a lower price and an already established user base.

If only...