What about, a 'mutator selector', at the end of every map, that selects a random mutator, and plays a few rounds with that mutator before map change.
Mutators include:
Randomizer
x10
Class Wars
Stock Only
Medieval (or non-medieval on degroot keep)
For maps, maybe:
Morrigan alley (PL) (medieval)
Cranetop (PL)
Cashworks (PL)
Traingrid (KOTH)