CyanogenMod developers have stated that they do not have access to the source code of Google Android Jelly Bean yet but it should not be a huge task to incorporate the new enhancements in their CyanogenMod 9 release.
CyanogenMod 9 is based on Ice Cream Sandwich. CyanogenMod 10 would be based on Jelly Bean.
Developers added that almost all devices getting CyanogenMod 9 would get the CyanogenMod 10 update.
CyanogenMod Team added:
With CM9 (and ICS) being such a large jump from CM7 (GB) we decided it would be best and most efficient to essentially rewrite CM enhancements from scratch. This added a bit of time to our development cycle, but the initial investment in cleaning our codebase has paid off, and CM9 is better for it. Now that JB is around the corner, we are in a place where most of our code will merge cleanly into JB, with minimal fuss.