Great game! Congratulations to you all! :D
I have a tiny suggestion (I know a little bit about game development so I think it would be really easy to implement): make the minimum kill cooldown 0 or 1 seconds, this could be really helpful to play "Custom game modes" like hide and seek.
Also, since people leaving because they aren't impostor is a big problem, a way to deal with it could be decreasing by 50-100% the chances to be impostor of players who haven't played a single match in the actual (public) lobby, and of course letting them know what's going on. I know it might be a bit hard to implement it, and also it probably isn't the best way to deal with the problem, but I hope you find this useful, even if it's just to inspire a better idea.
Thanks for reading! ^^