According to recent statements from the CyanogenMod team, they plan to have a quick turnaround for Jelly Bean. In fact, they expect to be able to convert all CM9 enabled devices to CM10. Here's a quote with a few more details,
It's pretty exciting that they expect it to be a quick turnaround. What is even more exciting is that if the CM team expects it to be this quick after having the .sdk for such a short time, then imagine what the OEMs should be able to do with it. We might have a much quicker turnaround for Jelly Bean than we did for Ice Cream Sandwich, since the work that OEM engineers are doing will also help them with Jelly Bean in many ways.According to a Google+ post which went up earlier this afternoon, the changes and new features introduced with Jelly Bean should be incorporated pretty quickly in the CM10 build, but some code changes for CM’s LockScreen enhancements, Theme Engine and Trebuchet will need to be made.
No promises are being made, but it sounds like CM10 should be available to all devices which have CM9 support. The CyanogeMod team isn’t discussing an ETA quite yet, but they do say that work on CM10 won’t truly begin until Google releases the source code for Android 4.1 and a stable CM 9.0.0 release is pushed out.