First off, this is going to become quite confusing for people less familiar with computer hardware. Intel has Z270, AMD has X370, and now Intel is going to have X299, and AMD is going to have X399/X390. But I digress.
X299 is a bit interesting as it’s going to have two separate ranges of CPU’s: Skylake-X and Kaby Lake-X.
Honestly the less interesting of the two, Kaby Lake-X will be limited to 4 cores and 8 threads, so basically you’re not getting an improvement over the standard Kaby Lake platform. In fact, it’s limited to 16 PCIe lanes and dual-channel memory, so besides maybe some extra USB and SATA ports versus the Z270 platform, I really don’t see what purpose Kaby Lake-X has. Maybe it’ll just have more power available to it for more stable overclocks? I’m not really sure.
Skylake-X, on the other hand, will be the next HEDT platform, and will now be expanded to include the first consumer 12 core, 24 thread CPU. It’ll also feature up to 44 PCIe lanes and quad-channel memory.
Of course the big question is price. I’d expect that the Kaby Lake-X chips would start around $350, because otherwise if they’re more expensive you might as well just get a 7700K. As for Skylake-X, who knows?
Taking past specs and pricing into account, I’d maybe expect the 7800K to be a 6-core for around $400, the 7850K to be an 8-core for around $600-$650, the 7900K to be a 10-core for around $1,000 and the 7950X to be a 12-core for around $1,700, following the 6000-series pricing.
Of course, Ryzen may convince Intel to drop their prices, considering that the 1700X and 1800X can obtain comparable performance to a 6900K for less than half the price. In that case, the prospective 7850K may drop to only around $500 to compete with the 1800X, but I honestly expect the 7900K and 7950X to stay at high pricing just because that’s what Intel has always done with their ultra-high end products. Although if AMD comes out with 10 or 12-core options on their X390/X399 platform that may influence Intel to drop the prices of those as well.