The CyanogenMod team posted this on Google+ to inform us about how the Jelly Bean update will work. Here is the full post:
Jelly Bean Status Update
Repositories for all AOSP projects have been created on our github to alleviate any potential mismatches (branch is ‘jellybean’).
While Jelly Bean won’t require a major rewrite of all the CM features, the source has been re-arranged and re-factored enough that a simple merge isn’t possible. So we will proceed with manual merging (this was to be expected really).
The plan of attack will be to cherry-pick everything from CM9 and fix the merge conflicts and relocations. It’s tedious but the only way. Ideally the original patch authors will forward-port their changes, so if you are out there and want to help out, join us in #cyanogenmod -dev.
+ Trebuchet might be messy to rebase onto JB.
+ Theme Engine will be messy.
+ SystemUI stuff will need to be restyled.
+ Lockscreen stuff will need to be restyled.
+ The current UX of Settings is good, no reason to change anything there.
A manifest (Cyanogenmod/android.git) will be going up later this afternoon, so the masses will be able to sync directly from our source at that point as well.
This will be it on the updates (so we can focus on actually working). Next post referencing JB should be when the merge/cherry-pick process is complete.
So it seems this is good news! It won’t take anywhere near as long as Ice Cream Sandwich! It might take a bit of time for them to get everything working, but the wait will be worth it. Imagine a future where every phone capable of running CM10 is capable of running at 60 FPS thanks to Project Butter. Now we wait patiently and not ask for ETA’s. Thanks CM team, for all your hard work!