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.