I wish we had more variety in coop instead of just bosses with 100% uptime.
Like the gray circle phases against Gate Keeper are a decent mechanic because it rewards coordination and aim (to a little degree anyway). I'd like to see more of that.
To take it a step further, what if we had coops that weren't just boss stages? What if we had gimmick stages with a variety of enemy types and the challenge was to speed clear?
What if we had stages that actually required using cover mechanics? Chatterbox used to be good for this because of his hit stacks but this is no longer an issue with Crown.
There's so much room to improve coop but I fear it will forever remain braindead because there are too many retards who don't like gameplay in Nikke.