komikoza Totally agree on this. It could be incredible and would add a whole lot of community driven variety to the game, but the amount of dev time that it would take just to create a public-facing editor let alone figure out a way to do the scripting for it (not to mention a large bank of reusable 3D assets that levels could be built with) would be huge. Even if users made their own 3D assets that would require a whole lot of effort to figure out storage and streaming solutions, sanitizing for any malicious content, extra moderation, etc. Still, maybe in the far future if they're able to, it would be awesome.
Ultimate Chicken Horse actually has a really great system for doing this and making it a cleanly integrated part of the game. Granted, it being a simplistic 2D game helps, but some of the user generated maps for it are everything from works of digital art to sadistic masterminds of level design, lol.