It's been suggested many times, last time IIRC with the 2 tube shotguns. The problem is doctrine. When it comes to less lethal ammo you want to be sure, really sure, extremely sure that it doesn't get mixed in with lethal rounds. IIRC police forces often use shotguns with bright blue furniture which are only ever loaded with bean bags.

This is one of those cases where the engineering is easy, but thr training/doctrine needed to make it work is far too demanding. Maybe some counter terrorism or high threat response team might consider it, but it isn't something you can give to average, even above average law enforcement personnel. (As long as you care about safety of course, Ruzzia used thermobaric rockets in hostage situations, so maybe an authoritarian state might use something like this to show their technological superiority over the west, while also proving their disregard for safety)