So i asked a high lvl doc to test out a few things on TEST as of patch 18.7.0.17
Haven't seen any mention on ubt resistance being removed on bosses so i asked him to test that inside miitaar.
Guess what?
He still resist.
What does that mean? You won't be able to init debuff bosses at all as they stuff every init debuff in the same nanoline, with the exception of LE -init procs i guess.
Doubt we'll get any comment on it and can only hope that there is still A LOT of stuff that's getting a treatment/modified before live, but now you know at least.