I notice playing that map that the waves start early (before all monsters are killed) and the last wave ends early too (monsters still alive when we win the match). I kinda like that and then I kinda don't.
Good points: keeps the game going without a pause. constant action. not having to search for the last rabbit.
Bad points: people spawn in front of titans from previous waves. result: splat.
Looking at this I can't help but think that maybe someone can create a mod to use some of these ideas. It would be nice if someone can create a mod that starts the wave when all action has stopped for a period of x amount of seconds. That way summoned monsters are not automatically killed off along with other monsters that the game "panics" on.
I know that I would like this because when I die and nothing is going on, i'm usually searching for that last rabbit and telling everyone where it is. with this kind of mod, that action would be unnecessary. And the good thing would be my summoned monster will not be killed off because a crawl is trapped in a hole that someone can't get to, then the computer kills them off.
My character skin -
If the Invasion Everywhere mutator is used it can keep monsters in the map all the time.
Haven't heard of anything that starts the next wave based on periods of inactivity though. Might be hard to code.
On the other hand, Monster Manager has some refined code for its Extreme Invasion gametype that does away with some of the bigger flaws found in standard Invasion such as searching forever for the last monster, premature wave starts, monsters that get stuck too far away to find, etc