It is EXTREMELY unlikely that FM3 will work on AM3(+).
It would even be unlikely to work on FM2....and here are some reasons why:
-FM3 will also be home to APUs. The power pin distribution/layout is very different due to the fact that a GPU also needs to be supplied with energy.
Thus AM3 falls flat.
-Zen CPUs are supposed to only have DDR4 support if I'm not mistaken. AMD is not gonna waste budget just to make it possible on older boards.
Thus FM2+ is also unlikely.
FM2+ is already not backwards compatible. FM2 CPU/APUs are only "forward" compatible.
AM3(+) is an outright antique chipset/socket. It's age is certainly showing.
Don't expect anything Zen related to work on anything but the new all-around socket.
Keep in mind that AMDs strategy is to fuse FM and AM together in this new FM3 socket...they want to unite all their platforms. I would not be surprised if AM1 style APUs also move on to FM3.
You know I find it strange that AMD will not release a 960K Athlon Carrizo.
Are we sure they won't do this? I think it was confirmed by anandtech? or is it a case that AMD don't want to excite the public and hence try to sell out as much 860K and 760K, seeing that Carrizo is so much better if people knew it was coming to desktop they would simply not buy the older models?
So AMD has plans on doing this but want to get rid of older CPUs first?
Carrizo CPUs would be a step backwards in performance. Carrizo is made with so called high density libraries. This allowed them to get a lot more transistors on the chip without shrinking down to smaller nm. Downside is that Carrizo can not clock as high as Kaveri...expect AMD to not bother. The only thing you can expect is a 870K. (The updated Godavari stepping of Kaveri)