I presume you mean
this multi-window feature? To the best of my knowledge ? and my Android knowledge is
typically accurate ? this multi-window feature only exists as a Samsung addition, ? la TouchWiz. Because of this, it's unlikely you will see such functionality coming with stock Android anytime soon. As for a community developer building this in to a 4.x-based ROM? It's certainly possible, but my guess is you'll have to do a lot of pushing or have a significant amount of support in order to see such an idea realized. Furthermore, the "multi-window" ability almost directly contrasts with ? and contradicts ? the method of multitasking and user interaction that Google has been pushing since 4.0, and refining in 4.1+.
It more or less comes down to the fact that in such a mode, screen real estate is
extremely limited for each application in question. There's a reason why Windows 8 tablets/desktops support it, yet it isn't present in Windows Phone 8. This is also likely a reason why Samsung introduced it on its tablets and phablets to start, and potentially part of why its smaller flagship phone, the S III, did not launch with it. On a device with a screen less than five inches diagonal, even with properly- and responsively-designed application interfaces, the basic UI elements such as the
Action Bar would take up a disproportionately large percentage of each application's allotted height.
Perhaps this was a
bit more detail than you were looking for.
TL;DR ? Probably not.
Edit: oh, and welcome to AC! It's an great place to be.