In any machine released today, I don't really want anything less than dual high-bandwidth (dual-link DVI class for example) output, so I really hope to see that in a forthcoming MBP.

If one of your displays is a high density 27" the other one may as well be too.

I do suppose it would be acceptable having the second GPU outboard on a cable or built into a display, but that would make it decidedly less portable.