I'd love to see more COOP/Invasion stages made.
That makes two of us. i wish i could help in any way. wait does Zandronum support lua scripting? that's how Sonic Robo Blast 2's getting by after reaching version 2.1 with new levels and a few new bosses. I might be capable of helping somewhat with this. but if not I understand.
I hope that you or someone capable of doing so also pays a bit of homage to Super Adventure Rockman. like having 3 consecutive levels each having a few robot masters per level and a battle with Ra Thor and Ra Devil at the end. i mean it apparently did well enough for Ra Moon to be a prominent character in the archie comics. so why not? =)