it's highly likely AM3+ will die after steamroller... (or even with the steamroller launch)... there seems to be no talk coming out of AMD about a continuation of the FX brand. If they do continue FX cpus they can probably do it on the FM2+ platform considering FM2 and AM3+ are identical sockets (well AM3+ is missing a few pins, but basically they're identical sockets, meaning an AM3+ chip will fit flawlessly in an FM2 motherboard, of course the fm2 motherboard would need a special bios to even recognize it.)
If they do continue steamroller with fx on AM3+, that will be the last chip on the AM3+ platform. AMD HAS stated quite clearly they intend to merge the AM and FM socket for DDR4... probably on an FM3, or AM4 socket (no word on the name of the socket yet)