The amount of RAM has no effect on the use of 2 APUs. You would still see a benefit in running the extra APU concurrently with the original APU. The OS could also turn off one the of the APUs when a game is not running.
As far as dividing the RAM up, we still don't know how the pool is shared. We don't know if each APU has access to the total pool, or if they a.ssigned a specific amount to each APU.
I don't see why the article would say that "it just changes the whole dynamics of next gen competition" if the extra APU was dedicated to just the OS. That really wouldn't change the dynamic at all.
I just personally think my guess of "1 6GB APU dedicated to gaming/1 2GB APU dedicated to OS & Kinect" is simply more realistic than dividing games up over two 4GB APU's. That just opens a whole nother can of worms for devs/porting etc.(see cell). I don't think they will divide it even if it's 2 4GB Apu's to be honest. 4GBS is plenty sufficient.
The article knows just as much as we do, so the quote is just shock journalism really. It's also linked to the original rumor of all of this, which came out on April 1st...