Hey Itch,
The co-op bundles feature is one of the most awesome features of the Itch, but I believe it has an issue that makes co-op bundles creation a pain in some cases, specifically, it's the restriction that disallows the creator to modify participants once the bundle is created. There is a lot of scenarios where the bundle can end up in a locked state due to one participant being unresponsive (and in most cases there is no way to directly message or find a contact of a person on Itch), considering Itch explicitly states it'll not notify the participant this makes it trouble sometimes to start the bundle.
I observed two solutions people use to work-around this - they either re-create the bundle or first create a gam-jam to collect active members willing to participate and then follow up with a bundle creation. These are clearly workarounds making the co-op bundle creation process challenging. If to add to this the fact that participants invited in a co-op bundle not being notified by Itch, it sometimes becomes a real pain.
My suggestions are:
1. Do notify people invited to participate in a co-op bundle
2. Allow to remove participants from a pending co-op bundle if they're being afk for too long