Especially with the shadow revamp I'm pretty sure they're going to push us out of peering into the void magics and find some nebulous explanation for our use of shadow magics.
It's an identity crisis because so much of a warlock was tied to this dread Legion that hung back in the background, and now that it's been simplified and dealt with they'll have to find a way to expand demon and fel lore beyond Sargera's Legion. And it's a shame because I still feel even at the end of this xpac the concept of the fel has been very poorly explained and Sargeras is being rather conveniently shooed away for some later reappearance in some xpac.
Even if Legion's demo was a disaster, I'm really going to miss my Thal'kiel. My floaty skull/head was one of the most unique artifacts and interactions with the concept of the power hungry summoner, and he's just going to disappear (other classes will suffer as well, it will be crappy for a death knight to go back to general swords that are not runeblades, so a warrior is using the same sword a death knight is or if a runeblade is introduced, a warrior or rogue will also wield it).