I just don't know about this Kaby Lake X. You lose the IGP, you get a smidge more base performance and a smidge more overclocking headroom, but none of the other advantages of x299.
With Coffee Lake on the horizon, and it requiring a new motherboard, will there be an x299 Coffee Lake X? If they can't make it work, which why would they be able to if they can't make the current socket compatible with Coffee Lake, then you will be buying a single generation motherboard for a fringe product. There isn't even the upgrade path to the i9 offerings.
As we've seen with Ryzen, Coffee Lake rumors, and i9, more cores seems to be the future, but this board locks you in to a platform that supports a max of 4c/8t, and with the prices being what they are in that segment it just isn't a good investment. It would make a lot more sense to release a lower cost x299 board with the majority of the features intact, including i9 support, and have an actual upgrade path to higher core counts.
If you plan on keeping your PC for 3+ years this makes SOME sense, but if you are an annual upgrade kinda person, stay away. We've hit a point where a quad core is minimum for any kind of performance tasks and hyperthreading only goes so far. It might last you for a while, but I don't see any kind of long term support in this niche, at least not the kind of support you will find on a mainstream platform or the larger i9 segment.