Something as small as a crippling wanderer nerf, and a Khanum Kha rework would make me happy. Course I have a fairly long wish list which I detailed in my fanmade balance patch. In order:
Wander/Kha Attention (Bare minimum to be happy.) > Small nerfs to ragnora and less face burn (including ziran, spellhai, and spikes), > extensive balance patch lowering RNG, polarizing cards, and uncounterable burst in general. > Actual new content.
Frankly I am fine with with very slow expansions (like a year or more) with the focus on balance with patches when really needed, allowing the meta to develop its self. The game is very close to great right now, it just has a small handful of crippling problems.
As long as said crippling problems get addressed I wont raise pitchforks and would be happy with the game for a very very long time.