Increase the amount of sources the game draws from, including mordenkainen and volo, for character backgrounds
Restore reaction spells to abjurers, incl durability of magical shields, and ensure that monsters like the Beholder Spectator actually get their reactions/Legendary actions abilities (dragons get them too)
include multiattack for creatures/PCs that can actually use it (Lae'zel should be able to, as all Gith warriors as per MM can do two attacks), as should the Intellect devourer. Astarion kind of does already. Thugs, however, don't.
Yes it would be very noce to see something like the hexblade warlock. From what I understand warlocks is a class wizards have been looking at as somewhat underwhelming in power but havnt done stuff fore like the ranger because so many players think they are cool and are prepared to overlook them being a slightly weaker class. The hexblade kind odresses a lot of whats missing from making warlocks semi melee viable casters. Looking at stats of what type of warlock people tend to play on a statistical level the hexblade is overwhelmingly popular and kinda shows the weakness of the other subclasses.