The weapon attacks are perhaps the only Larian homebrew I not only may not end up modding to 5e after release, but I will probably look at rebalancing and adding to them even.
I seem to recall older d&d having more options for melee than just swing weapon at enemy. Without bothering to go look it up, I seem to recall things like being able to do "called shots" which offered negatives to the hit chance to target body parts for specific purposes...ie a called shot to the eyes(-10 to hit IIRC) would cause Blind. I think Disarm was a called shot to the weapon hand. Things along those lines though honestly it has been so long now I can't remember it clearly. Personally I'd like to see the system in BG3 tweaked a bit and expanded on.
All attacks should require proficiency in the weapon to be able to use them.
I'd give penalties to the attack and unlimited use over limiting them to once per rest/combat.
Change the single weapon specific special attack to a "special attack" list. Any 2h weapon should be able to "Cleave" because you are just swinging the weapon in a big arc in front of you, it doesn't matter if it is a sword/spear/staff or club if it is 2h it gets access to "Cleave"(maybe rename this?). Any weapon can be used to attempt to "Topple" someone if you attack their leg specifically(this is especially needed imo since BG3 doesn't break "Shove" down into shove back vs shove to the ground(Topple)). I'd be interested in hearing other ideas for attacks that might be added like a Disarm maybe. So every weapon would have access to a few options for special attacks.
I do understand where peeps are coming from in that they don't want things becoming to "arcadey". But for things like Disarm(which is in 5e but not BG3) and Topple(which is an action anyone can do in 5e), I can accept those as special attacks. As for something like Cleave,if balanced with a penalty to the hit or what have you, than yeah to me that is something someone might legitimately ask a DM to try to do.