If you want to ask for a feature you should send a message to feedback@twitch.tv.
But i’m sure this would be a very low priority feature… The problem with IRC is that every message is send instantly, so to implement it you would resend another message, and implement it client-side to modify a previous message when receiving this kind of message… Also to prevent abuse from it, it would require to check in realtime if the sender of the command has the right to do it, and with a database of the size of twitch’s one you’ll get an impact performance side… I’m sure twitch IRC is enough unstable for now…