... it appears to me that the lack of hyperlinks is in the TODO list. But what about metadata (output-attributes)? Are they in the TODO list as well?
Anything not supported in Cairo but suported in the current backends is on the roadmap since a full switch to Cairo will not happen before it has complete feature parity with the current backends.
If you want more information on recent developments, and especially if you want to help out, you will want to write to the devel list and perhaps CC Han-Wen in particular.
Regards,
Jean