Title.
Extra missions for the campaign are nice and all, but they are pretty much the same ol’ gameplay, just different scenery.
Chaos Wastes is a lot more interesting though. Would pay for DLC for it, as I know the base is FLC.
I find myself on the opposite side of this. To me the campaign missions are what I like the best with Chaos Wastes a good alternative if the campaign grows stale.
Still I wouldn’t mind new content for either or both. While I’ve been having a break from Vermintide for a bit now, I can’t keep myself away from it in the long run. 
Im in the small group that doesnt like Chaos wastes very much and would want the map designs/dev time to be used for a main mission i can find via quickplay.