Both TAI and GPS time are offset from UTC by a noticeable amount, so switching to one of them would produce a large disruption, especially given that it would have to be done incrementally. Also, many people feel legally compelled to use UTC, so the only solution for them is to legally redefine UTC to have no additional leap seconds added in the future.

I wouldn't bother with leap minutes or hours either; instead we could just adjust timezones to create a virtual leap hour. It would effectively be a permanent version of daylight savings time (assuming that such a concept exists in 2,000 years).