Google has today added the Android 4.1 Jelly Bean code to the Android Open Source Project (AOSP). Assuming a worst-case scenario in which Sony has not been privy to the PDK would mean that Sony Mobile engineers will now commence working on Android 4.1 for Sony Xperia devices.
It should also mean that custom ROMs based on Android 4.1 Jelly Bean will start appearing soon. CyanogenMod has already said that nightlies of CM10 (based on JB) will up “once we are content with where the ROM is”. CM9 (based on ICS) will continue to be worked on though, the next release will be RC2 before the stable version is released.