Personally I feel like just elsewhyr is not gonna cut it if they really are working on their "most ambitious" chapter, probably elsewhyr+niben is a good line
Similarly, rest of hammerfall+colovia sounds not bad neither.
Skyrim or Blackmarsh won't be bad, but Skyrim probably should wait a bit longer to adrenaline hype again in future, and release whole blackmarsh right after muirkmire doesn't sound like a good idea, too repetitive and ppl are gonna rant "muirkmire should have been in the chapter in the first place"
And rest of the tamriel map (solthest, or telvanni territory etc) are simply too small for a chapter
So what's gonna satisfy you? Is one single province gonna cut it?