Here's an interesting idea for a game mode: abduction.
Basically everyone starts out as a crewmate. After a set amount of time (e.g. 3 minutes) a random person is abducted and replaced with an impostor and everyone is alerted. The game plays out mostly the same. Impostor needs to kill crewmates, crewmates need to complete tasks, you vote people out.
However, as time progresses, more and more crewmates are abducted and replaced with impostors until say, 1 or 2 crewmates are left. When that happens, the remaining crewmates need to either finish their tasks as quickly as possible or abandon ship. I call this 'run mode'. Also during run mode, voting is disabled. Anything I missed is up to you to decide if you add this to Among Us. You're free to change anything about the mode of course.