I actually looked, the Big East schools aren't that much further away from TCU then the Mountain West schools. The closest school in either conference was over 500 miles away from Dallas and I think the average of the new MWC was over 700 while the Big East was just over 1000. In terms of travel cost, it might actually be cheaper to go to the Big East schools, because the Big East schools by and large are located in major cities and thus TCU can easily hop on a direct flight from Dallas, while many of the MWC schools are in smaller cities (football may do private charters, but the other sports may not thus commercial flights may come into play).
Also, if Villanova says no (it has till the end of the year), then look for the Big East to make a hard play for Houston, which would give it a natural rival for TCU and open up even more tv markets. Central Florida is still possible as well, but USF doesn't want the competition in state.
I also think this is the beginning of the end of the Big East as we know it. I can't see the football schools continuing to say in the conference with the non-football playing members. Football is king and it will drive further expansion (maybe to 12 with Central Florida, Houston, and Memphis).