There really are several avenues I think could be explored. I'd like to consider coding an encompassing actor class that is a "spawn through" for different monster classes. This would allow you to make a map, add the spawnpoints for the creatures, then control them via an external file (like an ini). This would give you much more control of things and even allow maps to become reactive to internal influences. For instance if a group is doing too well, it could be set to spawn more/stronger monsters on the latter spawns to make it tougher.

I think that if you really want to move MH and it's family forward, it's going to start by going back to the basics and adding some more flexibility in the maps. That's one major drawback that needs addressed: the maps are boring once you have played them. They need the ability to change in some fashion to be less predictable or more competative.