Parmandur
Book-Friend, he/him
Monsters don't necessarily play by PC rules, though I could see a discussion of getting that in there as an option.One thing that I think they do need to implement in the MM is the new weapon mastery properties. If they don't -- if no monster is going to have these abilities -- it's going to feel wrong, cheap. At the same time, if every time a gnoll hits you with its flail you attack with disadvantage (sap), combat is going to slow down -- with an additional round or two, I expect, per combat. (That's based only on a handful of practice combats; it could be more).
I have not seen anyone else talking about the impact of Weapon Masteries in the hands of the monsters. A MM playtest would make that clear.