I mean this affectionately, but Ars Magica is a completely 1980s game in design (even in 5e) and as you say Unknown Armies is totally 1990s.

I kind of want to design an “Ars Magica heartbreaker” with streamlined rules, some formalisation of troupe play, and adventuring and lab phases where the latter doesn’t get taken over by bookwork. And the general magic rules are a bit lighter too. Not to mention the experience rules.

And a big “what you do” section at the start.