It's true that there coming out but there's no exact date, as for the OP's current CPU and the Ryzen 1200 the difference is quite significant (62%). Anything over 30% is noticeable so a 62% increase is quite substantial.
https://cpu.userbenchmark.com/Compare/AMD-Ryzen-3-1200-vs-AMD-A8-5600K-APU/3931vsm1766
There's also the 200GE which is the budget CPU for AM4 but at least this would put the OP in a new system that would fully be able to use that 660. With that A10 it would perform a little bit better but those APU's really aren't made for gaming since once you put a dedicated GPU in those iGPU cores get disabled unless they have a GPU that supports Crossfire with the CPU's iGPU. And even then the support is so poor nowadays it really isn't worth it. But if they can get that A10 for practically free then it might be fine to use in the meantime.
As for the B350 motherboard with BIOS updates they will be able to use the 3rd Gen CPU's and the only big difference between B350 & B450 is the memory support which the max for B350 is 3000 and B450 is 3200, 3rd Gen boards may support higher speeds but there's been little info. I suspect they'll give full details about the 3rd Gen CPU/MB's and exact release date at CompuTex.
I think I'm going for the Ryzen 7 3700X.