Not sure if it has ever been seriously considered, but would be an interesting mechanic to see ingame. RPG's are pretty great and having to have a little situational awareness when using them (ie not in small rooms) would be interesting.

I created a backblast mod in the original game using Sourcemod. In a 45 degree cone within a meter of the launcher, it would kill or heavily damage any players.

If there was a wall within a meter behind him, it would damage the firer.

Up to three meters in a 60 degree cone, I was going to have it apply the flashbang effect (never actually got this part to work).

I never finished the mod, because it ended up being a net negative on gameplay. The mechanic wasn't really helping add any tactical depth, and it ended up killing teammates in scores, particularly when bots would fire an RPG when in a group.

I'd think that this might be a neat optional feature for a hardcore mode, but generally I'd think it would be a net negative on gameplay.