PG-13 is the name of the game: you can be an infernal Warlock, sure, but the game funnels players towards using those powers in spite of the evil origins. A little edge lord, but within appropriate PG-13 parameters.There seems to be mechanical support in core 5e D&D for evil PC concepts.
The PH has an assassin subclass.
You can have a PC concept of selling your soul to devils for power. Or be a Cthulhu/Old Ones/Mythos cultist.
I found this quote in the DMG, page 92:
"Class Options. In addition to the class options in the Player's Handbook, two additional class options are available for evil player characters and NPCs: the Death domain for clerics and the oathbreaker for paladins. Both options are detailed at the end of this chapter."
Paladins no longer need to be good the way they were in older editions. They can be any alignment.
I have not gone through the Ravenloft book player options in depth yet but I would not be surprised to see something that could support an evil PC concept.
As for the future and what they will or will not put in the books compared to what they have been putting in, we will see.
For a Greyhawk setting book it would not surprise me to see evil cleric or fiend warlock suggestions for Horned Society and Iuz followers or the Great Old One pact for Tharizdun cultists.
I don't particularly think new options are all that needed to do Greyhawk though, the Scarlet Brotherhood monks are core evil monks, not close to monk mystical martial artists that require different rules to capture unique aspects of the SB. Would you give them political adviser things like a focus on intimidation and persuasion? The monster breeder stuff from the 2e sourcebook? More 1e style powers? Make up completely new stuff for them?