In astronomical contexts there are good alternatives to the epoch (like TDB, mentioned in another comment). I interpreted the top-level question as relating to

In astronomical contexts there are good alternatives to the epoch (like TDB, mentioned in another comment). I interpreted the top-level question as relating to day-to-day measurements and representations of time, presumably for use by extraterrestrial humans, since the commenter asked in the context of handling time zones and units like weeks and months which are irrelevant in a scientific context. UTC is not a great choice for a universal interplanetary time system, as it's designed to work on just one planet, for just one calendar system. It'll work fine while we're asking humans on Earth to oversee robots on the Mars, but will fall down pretty quickly once humans take permanent residence on celestial bodies that don't have Earth's rhythms.