You might be interested in this thread from XDA. Its a software that you install on you computer that makes almost any app have the ability to have multi-view. Does not require root, just JB and mutli-view.. I think it doesn't work on system apps (gmail) unless you are rooted.There are also threads where people have already modded some apps with this tool. Honestly I'm not sure why all of the mobile operating systems were not built with this from the beginning. Works on all devices that have mutil view after JB update.
This easily makes the Note 10.1 the best tab on the market until others copy it. There are a couple of videos on you tube that show off the feature.
Here's the link
[Tool] Add Multiwindow-option to almost every apk files - xda-developers
Here's a link to the list of apps that people have already converted
[APP] Multiwindow Apps - xda-developers