Could always put a pi or a noac in it, though pretty much anything you do with it will either need one of the screens off all the time, or fill the hole with something else...
Edit: ok, I felt as if I should add something of value to this post. DS shells don’t lend themselves nicely to projects due to their size. As cheese mentioned, a Pi or NoaC should fit inside pretty easily. If you do that, I’d suggest pulling out the slider stick and screens since sliders are popular in portables now and the screen could help a neighbor who busted theirs. Another “fun” idea is to attempt putting another model DS inside the old cheese wedge shell.