I just don't see red lightning and sha as being anything to do with warlocks. It's dark, sure - but so is everything a Deathknight does, didn't take anything away from warlocks. Warlocks aren't just a collage of everything dark and edgy in warcraft.
Warlocks to me are the existing 8 years of demon summoning, fire and shadow magic, not sha which have popped up in the last month - I don't see how giving new elements to other classes removes any of the flavor of a class that has existed for 8 years without them.
Sha I don't think anyone should be "getting", they're portrayed as uncontrollable, leave them as that. Spriests can get their fun cosmetic item this tier, but I doubt it will last longer than that, just like the Firelands flame staff wasn't some move to give druids fire magic. But, if sha did go to anyone - I'd consider it more sensible to be priests than warlocks.
Blood Magic I can kinda understand - we've had a fair few blood themed spells and a blood themed tier, but we're also not blood mages (who seem like the halfway step on the blood elves fall into using fel magic). I would be disappointed if mages ended up getting any blood magic - since I agree that's stepping too close into warlock territory, but I don't really see that happening either.
In short, I'm completely fine with other classes using dark-ish schools of magic, provided they don't step into the warlocks domain. We don't have a monopoly on dark magic any more than paladins do on holy magic, shadow priests have been using it forever and Deathknights are plenty dark without stepping on a warlocks image. Blood is probably going too far, but that's all purely conjecture.