There's no telling what the 8700k will cost at this point. It will likely have faster per-core performance than a 1600, but if it costs twice as much, the 1600 may still be the better deal. At the very least, it will almost certainly cost significantly more than the quad-core 7700k, and that's currently a $340+ CPU. Meanwhile, a 1600X is around $230, or a 1600, which can overclock to similar levels, can be found for around $210. It sounds like there will be 6-core i5s as well, but those will lack hyperthreading, only having 6 threads.
Really, a lot of it comes down to what the CPU is being used for. If it's just for general desktop multitasking use, having 12 threads might not even be necessary. If it's for gaming, the higher per-core performance of the Intel chip might be a little better. For heavily multithreaded use, such as for video encoding, an 8 core, 16 thread Ryzen 1700 will almost certainly cost less than an 8700k. It would be hard to make any sort of real recommendation until Intel's 6-core i7s and i5s are out, and have been priced and benchmarked though.