Formats like NSF, SPC and GBS are supported by numerous players including even Rockbox.
This would be a request for the media player frameworks themselves: Phonon or GStreamer. Probably GStreamer would be the best place to request this.
There's already a gmedec GStreamer plugin for them though.
Changing status until some developer confirms whether Amarok has an internal list of supported file formats, or requests them from underlying components (at least the FFmpeg library supports game formats). > Phonon or GStreamer Feature requests for Phonon would be tracked at this bug tracker.
Formats are entirely dependent on external libraries, be this Phonon, Gstreamer, VLC or taglib