Dry dropper or double dropper rigs are common in a lot of western salmonid waters, as many here who've fished out there know. Some states limit you to 2 hooks per line. Barbed v barbless? depends where you are.
Certain, umm, State Entities have legislated barbed hooks out of existence on certain waters, and one or two have tried the single point, single line, barbless only route on major waters fished concurrently for multiple species. And even that depends on what day it is, where you are, and what seasonal fish you're after. It's a nightmare for the fish, the fishermen and the enforcement folks.
Trebles, especially weighted trebles, are considered illegal snagging gear some places when not fished as part of a lure. Thats why you'll see guides for steelhead or up river brights in places like Oregon or southwestern Washington remove the trebles and add a larger single point barbless hook instead (Exception Alaska, theyre allowed to snag in order to fill their larders)
@flies&brookies; you're not seriously thinking of proposing a single point, single line barbless rule, are you?
Also, was going to PM you some info for research examples, but your personal contact restrictions won't allow it.