Yes i think it's possible. This game does not even use dedicated servers.Is it possible for the devs to simply make a controller/AA playlist for Crucible?
I don't mind Aim Assist on PvE content, but having an advantage during competitive multiplayer is unacceptable IMO.
The main argument for Aim Assist on PvP seems to be "Destiny isn't about competitive multiplayer" but shit like Iron Banner says otherwise. Pit all the aim assist users in their own playlist, problem solved.
All they need is to check which input method is used during matchmaking and make a toggle or checkbox in menu "Matchmake only with gamepad players YES/NO" or few different icons in Director for competitive gamepad-only crucible modes. They already doing this check to switch button prompts to match input device or recoil model. If it swaps from gamepad to M/KB during match just kick player from game/not allow to move until switched back. There will be m/kb cheaters just like on consoles, but i think this is not a big issue.