Both devices will be stuck on Android 4.1.2 Jelly Bean
It looks like it's the end of the road for Motorola XOOM and Nexus S as both devices will continue to use Android 4.1.2 Jelly Bean platform instead of the newest 4.2 version launched this week.According to Jean-Baptiste Queru, technical lead, Android Open Source Project, “there is no support for 4.2 on Nexus S and XOOM. Those devices should continue using 4.1.2. I can’t comment about the future of Nexus S and XOOM, sorry.”
After this statement, there's nothing else we can tell, but we can only hope Google will find a way to offer Nexus S and Motorola XOOM owners a glimpse of what the latest version of Android has to offer.
For the time being, Android 4.2 is available on Nexus 7 and various versions of Galaxy Nexus. Stay tuned for more updates on the matter.