UTC and TAI are off by over 30 seconds; people can't accept a discontinuity during the switchover. So what we really want is something like TAI-35. But the real problem is coordinating everyone to switch timescales so we don't end up with half the world on UTC and half on TAI-35. Also, I've heard there are cases where people feel that they're legally obliged to use UTC because that's the legal definition of civil time.
TAI for the timekeepers and as an internal representation, UTC for display, much like how many computers keep time in UTC and apply an offset to display local time. Just because we have to deal with the legacy of POSIX doesn't mean this isn't the right solution.
Yes, there are the obvious problems like the uncertainty of scheduling future events in UTC because the insertion of leap seconds aren't known in advance. But such things should be scheduled in TAI, anyway.
