The solution is obvious: put a .metadata in the bootable partition and
fill it with stuff like:
OS_NAME: Fedora 11
I would call that a trivial task but someone with some "standing" in the
community should ask other distributions to do the same in the same
format (and encoding and other technical stuff that matters) in their
own install process.
Then
a) write a patch for grub to handle that, or (if grub is not able to do
so, what would be weird)
b) write a small tool that detects bootable partitions and generates
boot entries from that metadata files (and "unknown" if it's missing).
\me just wonders why nobody already did that stuff