Loving the premise of this game so far and we only know just barely the tip of the iceberg. Playtonic emphasized that they are truly catering the game for the fans and that they wanted fans input.
Seeing how the game will come out on PC, how about a way to import our own levels/have a way to create our own worlds with their engine?
This way after we complete the game and find all the secrets we can then create our own worlds/secrets in Project Ukulele. It may be tough to implement having an editor for the game, but imagine how long the games life can live past release.
The only flaw I can hear people say is, what about if the game wants a sequel, people can just make the new stuff instead of buying the new stuff? Playtonic Games are full of creative minds and the sequels or new IPs will be fresh from the engine Project Ukulele will have, so it'll be different, also it'll be a new experience!
Fellow game developer designing a 3D platformer...a hint of the character is my avatar!