Lots of folks use Amethyst which does this, some folks use the testflight beta of Nos which also does it. I think compiling a list of which nostr clients do what for reports / deletes / content warnings and the like would be useful.

I believe other apps do. I know Primal has some pretty good moderation features in their web app version.

One big issue is that folks think a report is somehow going to trigger some unknown agency to remove their content rather than realizing that it’s just a content warning for the followers of the person who made the report. We need to update the language just like we changed block to mute.