I'd see this maybe as a sort of addition to the mini-game gui, which would add an option to enable/disable waves, how long they last, and how many there are. Each wave can be customized with a sort of caller that does things to certain bricks, such as maybe a infinite zombie survival. The caller would tell a named brick what to do when it hits that wave. It could be used to make a difficulty meter, and it raises as each wave goes on. I could only see this useful for infinite zombie invasions of anything to do with a unlimited survival that ends with all players dead.
tl;dr: A wave system for invasion related mini-games with call functions for bricks in each wave.