I agree that the ban isn't very likely and even if instated it would almost certainly have a grandfather clause.
However, I do think that manufacturers would be quick to find a new market going forward. Just like they have flocked to the "tiny-niney" over the last several years, I think that we'd start seeing a lot of new single stack polymer's that are effective for both carry and competition.
For those who pointed out that a larger grip and sight radius improve practical accuracy....thanks, but I kinda already new that. My point is simply that the gun makers seem to play numbers games now and I think that larger calibers and new single stacks would become the rage.
For instance, a new shooter could buy a Glock 34, but then someone would come up with something that has the slimmer dimension but offers all of the same pro's and suddenly people would stop feeling like the Glock was a "no brainer". Beretta 92's would get overlooked for 1911's. Why buy the fat design when there are slimmer designs that do the same thing.
Gun manufacturers have become masters of starting new trends and I'm guessing that's what it would be. (note: I like this trend! We've gotten some great products out of it! )
Just my $.02