The price of the cards I use for GPU mining initially cost me $270 per. Comparable cards cannot be found on newegg.com, and the "out of stock" price listed is >$500 per card. AMD and NVIDA cards are just not competing. My bet is that ATI knows exactly why their cards are selling so well and would be willing to create low cost ASIC, FPGA, or GPU hardware specifically targeted to mining. If I were NVIDA or AMD, I would be searching for ways to cater to this market as well.
If you are really concerned about a threat to FPGA centralization of computing power, start an email campaign to NVIDA and AMD asking them to create hardware specific cards to meet our mining needs. All that is needed is a bit more competition.
EDIT: Cleaned up awkward wording.
I'm sure some product line manager at AMD has noticed the strange selling out of 6990s and 5970s, and if they have even an ounce of grey matter they've deduced it's the result of Bitcoin. But to support the development of a custom ASIC by one of the big boys, the card sales volume needs to be truly astronomical. I don't see Bitcoin really changing the course of NVIDIA or AMD until there can be provable demand for millions of such custom cards.
In the mean time, there is definitely a niche market for a custom Bitcoin ASIC, if someone can get the job done profitably.