IDML or INDD export would be nice as well.
I know it's probably unlikely given its likely complexity, but several of my clients require work in that format.
InDesign is the only app keeping me subscribed to Creative Cloud, and I would drop it entirely in a heart beat if Publisher became a feasible replacement for this workflow, but without being able to hand off working files in an InDesign format, I just can't use Publisher as much as I would like.
Definitely needed. Still waiting for RTL support, though!