I hope people realize that the transition to 28nm means they can fab the same GPU on less silicon. A die shrink doesn't mean they're going to fab a GPU with the same surface area as a 40nm GPU but with 85% more ALU's, because that wouldn't make sense at all.
Odds are they're going to use the die shrink to crank out a higher number of GPU's to meet (hopefully high) demand. With the move away from VLIW, it's anyone's guess as to how the on-die real estate will get divided up.
I hope you realize what you say is utterly sutpid.
ATI has no problem makin as many 6990 as they want - the problem they have is that this does not happen "at will" and they simply scheduled too little capacity on those chip lines. You can bet you ass that they will scheule larger percentage for high end cards of the 7xxxx cards are better than the 6xxx series for mining (which they will be) to accomodate the increased miner usage.
But, again, once scheduled this is not really the problem -as can be seen by the amounts of 6970 available on distribution channel.
What is more criticla is that they are in a struggle with nvidia that is to a large degree decided by speed. So, getting a 28nm card out, beforre nvidia, they will make sure they kill there. They likely will make chips that are significantly faster than the 6xxx series (and no, 85% is not the number... we talk of 185% more density), also ramp up the speed (which is a side effect of smaller structures) and come out with something 2-3 times as fast as the last generation (the question is whether this will also be integer performance). THEN they will also use a little less power - and start killling NVIDIA as competition as long and as strong as they can.
Doing what you says would mean they totally loose the competitive advantage of moving to 28nm before Nvidia. it is so utterly stupid it would result in the board of AMD getting letters from some lawyers from their shareholders for destroying corporate value. This is not a struggle for yield and production costs for a large part, it is simply a struggle for performance.
This is, btw., the same thing that always happend with the exception of the 5xxx -> 6xxx transition which was a really bad thing - basically the 6xxx series was supposed to come IIRC in 32nm, but they could not get the production process reliable in time, so they went with the same "old" process and got stuck in 40nm like the 5xxx series. Bad timing. This time they are early - earlier than Nvidia - and I bet (as in: buying AMD stock vs. Selling Nvidia) that they will use it for some really nice marketing spin.