Can I create posts on behalf of another user via REST?

Great point. I had not considered the angle you raised in the second paragraph — it reframes the whole thing for me.

Tried this on a staging copy first and it behaved exactly as described. Confident enough to roll it to production now.

I respectfully disagree on one detail. In my setup the opposite held true, though I suspect it comes down to community size.

We ran into the same situation last quarter. What worked for us was starting small and only adding complexity when a real need showed up.