Custom Skins. ( The ability to use user images as backgrounds, this way users could skin the app to look like any hardware controller , all they would need to know is the pixel dimensions of background panels.)
This is definitely under consideration. Right now the problem with custom page backgrounds has to do with memory and how the backgrounds (and pages) are cached for efficient page switching. However, these problems are probably surmountable and I'll be able to provide this at some point in the future.
Also see: /qa/86/can-import-own-backgrounds-skins-for-controls-midi-designer