I'm pretty sure the reason they haven't gotten anything like that is that they have the worst liked aesthetic out of every army according to all polls I've seen on the subject by a wide margin. Even then they still got spells and terrain at least
Dark eldar no unless you count the refresh on drazhar and incubi as expansions.
Tau admech are not likely to get a significant expansion. Chaos space Marines are likely. I don't think psychic awakening indicates any sort of renewed focus for the army, same with broken realms.
Both are sisters of battle characters.
Other armies in psychic awakening to get characters were orks, thousand sons, chaos space Marines, Marines, Tau, elves of course, and admech got a wave