What is blocking a new D6 release?

The D6 release is >2 years old now, so what is blocking a newer D6 release?

Are there no relevant new features or bug fixes in -dev?
Is -dev particulary unstable? (We are using it in production, so the answer to that is no).
Which issues need to be fixed in order to provide a new stable release?

Pardon me for not having diff'ed the code, but perhaps someone has simple answers to the above, before I go research.

Cheers,
Achton.