Google has released Android 4.2 Jelly Bean source code to the AOSP yesterday, this mean that third-party ROM are getting closer from everyone. Meanwhile, Google Nexus 4 and Nexus 7 3G do not support AOSP due to the lack of GSM authorization. Even worst, Nexus S and Motorola Xoom may no longer support Android version later than 4.1.2.
In more precisely statement, these two devices will no longer support the official upgrade to the latest Android version. But it does not mean the unofficial support for these devices will stop at this state. We believe that CyanogenMod team will provide the next generation platform upgrade to these two devices. Nexus S and Motorola Xoom users may need to wait for the release of unofficial 3rd party custom rom. You shall taste the same as Nexus 4 soon.