I found Solasta repetitive, and the narrative is sometimes hilariously bad, but mostly just bad.
The mechanics of combat are functional, and as a dungeon crawler is decent to a point. It quickly becomes repetitive though, and a lot of the other systems - travel, etc - are not good.
Outside of some of the combat interpretations and implementation Solasta (reactions, etc) has I don't think there's anything in it that BG3 should look at.
Noted that I've not played Solasta in over a year. And have no desire to go down their DLC path to play it again.
Your points are understandable.
Other things that BG3 could copy:
Flying beasts .... they nailed it!
Walking on walls and ceilings....Larian could one up that one. If only we could look up to something creepy staring down at us from the ceiling...maybe they are there now :O.
Bosses with epic actions ... nailed it! That would include Dragons and Spectators...as they wind up for their nasty attacks.
A module maker...Sell it as an extra.
Prof. Dr. Dr. Mad S. Tist 
