There is not nearly enough for a functioning N5G Rockbox port. We're still missing a ton of peripheral drivers, power saving, and a flash translation layer implementation. Not to mention there's currently no untethered code execution exploit for the N5G.

The N3G/N4G have an old WIP code dump from years ago, and that's in a much better shape to pick up and try to get upstreamed into Rockbox :).