I've spoken with several folks about this. I believe you'll see a big increase in ticket sales, but the folks in those seats won't be wearing purple. I think some TCU folks might be surprised that the guy they've been sitting next to for the past decade is actually a Horn, Sooner, Raider, Bear, etc.
From the standpoint of putting people in the stadium, it will be a big positive. Only issue is that those 40,000 folks who wore purple to watch TCU play Utah might only be 25-30,000 now.
One other thing you'll likely see is that less of Fort Worth (or at least the area of town nearest TCU) will get on board with the "backing the home team" mentality. The TCU "wear purple Fridays" will take a hit. I know several folks who've said that rather than sending their kids to school wearing purple on those days, they'll now be sending them to school wearing their first choice schools colors, be they orange, red, black, or green.
I think one paradox is that TCU could be a victim of their own success. I think most Fort Worth people will be inclined to initially continue supporting TCU as their "home team". However, if TCU walks into the Big 12 and starts winning, it will be at the demise of the schools where these folks loyalties really lie. TCU beating OU, UT, Tech, etc. could push fans of those schools off the TCU bandwagon in droves.
Regardless, I think it's a great thing no matter what happens. There will be excitement around TCU football games every week that has only been seen a handfull of times over the past several years.