You will never see that on the FM2 platform, everything AMD is putting money into now is budget, mobile, onboard GPU and power savings. The FX chip stuff is going the way of the dinosaur. They gambled on multicore years ago and realized that was a horrible investment.
1) They most likely want as big of a gap as possible between 8 core FX and Zen, to add more excitement to the launch and get more people to open their wallets for new motherboards and such.
2) Their current CPU people are probably not the same people who favored the CMT SOI design philosophy. So, instead of making FX look better, they'd rather just have it look worse by leaving it with 2012 design and 32nm all the way up until Zen finally is released.
The problem with these strategies is that Intel is selling stuff at a greater rate during all that time and people may not be willing to buy new motherboards and RAM once Zen finally does ship if it's not really better than what Intel is offering.
There is a small market for AM3+, at least, 8 core FX chips with an improved process node and the improvements to the chip design that have been rolled out on FM2.
I think it might add even more brand loyalty to give AM3+ one more minor upgrade option (28nm FX 8 core with the improved core design) since Zen is going to take forever. It's not like DDR4 is really an advantage for anything but power consumption which is only an issue for servers. Such an 8 core FX would also make AMD look better after the 9590.
Whether or not it's a good idea to roll out a better 8 core FX on FM2 or not I can't say. I doubt it, though, because the boards are probably not made for that level of heat and power consumption. But, I don't know much about FM2 boards.