In a similar fashion to how games like Super Mario Maker thrive and because of Phantasy Star Online 2's procedurally generated quests in the past, I do feel this can be an opportunity for players to create their own Cocoon challenges and dungeons for other players to play.
The goal for me is not to get a reward at the end (potentially something like "FUN" points or the equivalent?) but rather that I like the combat and the action of the game and I like being put in situations where I may have to adapt to what the person who created the challenge is testing me for.
The basic idea I had in mind is that players would be able to create a map using tiles provided by Sega, be able to set enemy spawn patterns, objectives (defeating enemies to move on, defend a point for a period of time, collect a certain object to unlock a wall/door, and so on), and additional parameters like a time limit, lives limit, player count limits (solo-only, a number of players such as up to twelve player dungeons), and more so that players can create a dungeon to play through and share with others. I feel this can be something that players can engage in to simply have something to do as an alternative to socializing in the lobbies or waiting for Personal Quarters/Alliance Quarters to make some sort of return.
If it had to be extended or expanded further, I would absolutely love to see this take on the nature of allowing players to lay out and create dungeons using the styling of the original Phantasy Star Online 2 locations and use even their enemies and content as a possibility (such as Naberius Forest for example including bosses from the Divide Quest rotations). At least in the in-game sense, if we have NPC's who are capable of creating virtualized environments for us to practice, I do not see why we as players can't create challenges for one another or for ourselves as well.