The problem is the ACC's weak football brand and that outside of Virginia and North Carolina, it has no #1 team in its state. Pitt is no PSU, Clemson is a bit behind South Carolina, Georgia Tech hasn't been close to Georgia since the Bobby Dodd days, Florida State and Miami invariably trail Florida, and Louisville may be ahead of Kentucky in football, but so what?
I'm a Maryland alumnus who's glad to be leaving the ACC for a conference with a real, old-money football culture; I can't imagine anyone in Austin would be thrilled about playing Wake, Duke and BC in football every few years.
Also, in terms of distance, it's not as if the ACC is next door to UT. The closest members would be Louisville and Florida State, probably not that much closer to Austin than WVU is to Ames. Distance would be a problem for Texas in switching to any major conference -- the least difficulty would be the SEC, but A&M probably would have veto power and from an academic perspective, in the SEC, UT would feel like its IQ was shaved ten points.
I doubt the entry that opened this thread (UT and Georgia Tech to the Big Ten) has any possibility of happening...but let's say it did. Tech is AAU, just like Texas. Atlanta is a wonderful city to visit, easily accessible by air as the "crossroads of the Southeast." And adding both the Longhorns and Yellow Jackets gives the Big Ten a legit one-two punch in baseball, alleviating some concerns and perhaps persuading some current Big Ten members to bolster their programs.
Unless Texas maintains the status quo and remains in a withering Big 12, it won't be calling the shots in its new home. Perhaps it could to some extent in the Pac with Texas Tech, Oklahoma and Okie State, but not in the Big Ten (it's an all-for-one, one-for-all philosophy traditionally alien to Austin), and certainly not in the ACC (as Notre Dame will discover when it locks heads with the Research Triangle schools, particularly UNC -- it thinks it's an alpha dog like Texas without alpha dog football). There will have to a change in mindset in burnt orange country, no matter where the Longhorns move.