> Now if I want to write software that uses precise TAI, I can't do that because of broken UTC from time servers and TAI is defined as UTC+tai_offset on my side.
Yup. Even if your NTP UTP source is perfect (lol), there aren't any cryptographically authenticated sources for the offset as far as I'm aware. (and NTP doesn't carry even an unauthenticated one).
GPS carries an offset between UTC and the (leapsecondless) GPS timescale... but the GPS signal is a bit of a pain to get to, and also unauthenticated...
