Yes, I would say that is critical. It’s not a big deal to me if Discourse doesn’t support Facebook video. It’s a big deal to me when a member pastes a link (hardly unusual) and it produces an error message… and the original link is gone. I have several messages like this in my forum now. Us admins are manually fixing them as we see this but obviously that’s not a great solution.
I believe this is a serious bug, only in that Facebook (along with other videos sites I’ve tested it with) is wildly popular.
I would love to figure out a quick fix… let me know if I can help?