A theory I've seen (totally unsubstantiated) is that they'll do a round of "dark/antihero" subclasses in the DMG, like Death Cleric, "Oathbreaker"/Oath of Corruption* Paladin, and Necromancer Wizard. Assuming it (a) still exists but (b) won't be in the PHB, I could definitely see Assassin Rogue being slipped into that group instead.

*Trying to manifest this rebrand into the universe