As I have multiple rockboxed ipods, one thing I'd find useful is if I could give each their own bootscreen (so it's easy to see 'this is the podcasts-only one' 'this is just music', and so on). I suspect, maybe, there's a reason why the bootscreen is embedded in rockbox rather than an external image file - perhaps it avoids a possible point of failure or keeps the core of Rockbox smaller or something? But if it were possible to have that screen as a customisable .bmp file I'd find it useful.