1) This is a programming question, not a request for help with installing Rockbox.
2) This question isn't exactly Rockbox related, we're quite happy with how the current Rockbox bootloader works. It's not intended to be graphical, it's intended to be simple and fast, and boot Rockbox. Dual boot is more of an 'extra' to help those who need features Rockbox doesn't yet have than something that is likely to ever be developed much further for multiple boot options.