Name a single DLC for the past 3 TES games that added gameplay features instead of quest/items/areas.

(the answer is none)
Hence the "I Hope"...

uh... anyway...
The little bit of working information we have on this subject really doesn't help anyone to conclude what exactly we should be expecting, due to vague statements and little insider information.
That is to say, that we could get absolutely bloody anything.
Heck it could be a weapon pack. It could be 2 races. It could be the Hot-coffee of Dragons... we just don't know yet.