Is there currently a way to have a preview crop mask in the render viewer (and viewport as well for that matter?)
Imagine it'd be a fairly straightforward thing for SideFX to add if it doesn't exist already, but wanted to ask the community if that already exists somewhere but is currently hidden?

I just want a display crop, not a render crop…

I would say submit it as a bug, as it's clearly working when you render to MPlay, but not in renderview