Honestly I think they should add Hexblade.
What would be great is if WoC recommended what subclasses should be in the game, based on their own evolution. It's clear some subclasses in 5e are the "natural improvement" of older subclasses.
I really want Hexblade too, because it's such an interesting departure from the normal warlock playstyle.
It is cool to have hexblade indeed, but we can be sure only with PHB subclasses, and so, BG3 needs to have overall update to Pact of Blade. As for me, it is strange, that cha to weapon rolls is not pact of blade feature by itself in 5e. Hexblade even get 2 abilities at 1 level, when other patrons gets 1 (Celestial gets 2 abilities too, but light and sacred flames cantrips addition is just icing on a cake). I always homerule pact of Pact of Blade cha to weapon rolls in my home campaigns
