The problem isn't really about handling local time. UTC is an offset from TAI and time zones are offsets from UTC, it's overall really just an offset from TAI.

The problem isn't really about handling local time. UTC is an offset from TAI and time zones are offsets from UTC, it's overall really just an offset from TAI. Coordinating the TAI-UTC offset is not any worse than coordinating time zone offsets. The complications are around clocks, UNIX timestamp and NTP, where a steadily and monotonously increasing number would make the most sense, and that's not UTC.