Nothing stops them from hosting it on fbi.gov, state.gov, etc.

It's one thing to block some random .gov site unused for anything else, it's another thing to block a domain used for, say, filing flight plans.

Since no one seems to have a serious answer to this…the answer is yes, it would easily be blocked. Beyond that, absolutely no one would use this service. Therefore, it can be considered to be nothing more than political posturing by a weak administration.

They wouldn't dare ban a .gov domain and we will hide all of behind Cloudflare! /s