Inb4 "a MMO can't have level editors!" City of Heroes has one.
Ok so here's the idea. Create a level editor that we can access. Since Spiral Knights is a fairly simple game I'm sure the interface for it wouldn't be that difficult. You'd just pick a background/tone (like forest, or road, or whatever). Then you'd start off with a blank slate (or maybe have a big square to start off as a starting point). Then you could place various things like gates and what type of monsters spawn and spikes and switches whatever. Then you could put things like how many floors it has and then edit each floor.
A downside to allowing people to make things though is trying to make a way to get easy money. However if you create a system that regulates what you can do (like instead of placing each particular monster you just tell the game what type of monster you want like gremlins or goos) then it's not a big issue anymore. Another issue could be that nobody really plays the normal levels anymore that the devs made. So something that could be done is that you can't place treasure chests or merchants in your levels or not allow monsters to drop equipment/materials.
A neat thing about this whole system is you could integrate it into guilds. You first however would have to make it so you can actually do things with the guild. But you could make it so guild members can access maps that your guild has made. And then you could make it so you can place minerals in the levels. Then make it so any mineral you get from a player created level is donated to the "guild bank" that can be used to construct things like NPCs (like a travel NPC that you use those travel passes for) or structures to just make your hall look cool and unique.
I think having a level editor in conjunction with guild features could make for a really really cool system.
Edit: Oh and make it so these levels don't use energy, or at the least uses reduced energy costs.
I think that a level editor now would be great, as we could test thing far more easier and faster, as we are now in closed beta, and this is what we do. But, after the full release, it should be removed (instead of the guild ones), because it would not serve as right.