Coffee Lake's dam burst, and the trickle of information we've seen over the last month has turned into a flood. The latest information comes from ASRock, which published Intel's imminent Coffee Lake CPUs on a Socket 1151 compatibility list. We grabbed a screenshot, but ASRock later removed the Coffee Lake CPUs from the list.
We already knew that Coffee Lake requires new 300-series motherboards, as first indicated by ASRock and then later accidentally confirmed by Intel, but sticking with Socket 1151 will make it harder for enthusiasts to stomach the lack of backward compatibility with 200-series motherboards.
This isn't an entirely new tactic from Intel, but we need a good reason to upgrade from the eight-month old Kaby Lake-era Z270 motherboards, and in contrast to Intel's other transitions, this time around you will gain extra cores in the process.
That comes with a caveat though, as we would like to see some additional platform capabilities from a new chipset, but all signs point to the 300-series chipset merely being a "Z270 refresh," meaning it will not bring any increased connectivity options. It remains to be seen if the 300-series will support Kaby Lake processors--they do share the same socket after all. But outside of new LED functionality or other third-party additions, that might be a dubious upgrade path if there aren't connectivity improvements.
ASRock's specifications generally line up with information we've posted in the past, although we do see the Core i3-8350K listed as a 91W part instead of the typical ~60W we see with the i3 series. This is either a typo or due to the extra two cores.
ASRock also listed the Core i3-8350K with 8MB of cache and the i5 series with 9MB. Previous information has indicated 6MB and 8MB of cache, respectively. The listed specifications actually make more sense, though, as the i5 series usually carries a 1.5MB allotment of cache per core, so that would line up with Intel's current approach. The i3-8350K's 8MB also lines up with the i3-7350K's 2MB-per-core alignment.
More information is emerging weekly as Coffee Lake moves closer to market, which follows the normal trajectory of leaks as motherboard vendors finalize their products. Many of the leaks are dubious, as usual, but when vendors slip, we can assume the information is more reliable. We are certainly on the cusp of the Coffee Lake era, and although Intel is adding more cores, AMD is the fly in the ointment. AMD plans to support its Socket AM4 for all of its processors until 2020, so Intel’s lack of backward compatibility with existing 200-series chipsets will likely dominate the conversation.
If you're looking to build in the second half of next year I can assure you all of this will be irrelevant by then. I'm willing to bet the 300 series mobos will be a one and done. 10nm Cannon Lake Chips will be out by the time you're looking to build and I would suspect they won't go into a 1151 socket or 300 series board.
HEDT platforms are a waste of money and no more future-proof than mainstream platforms if you aren't going to need their HEDT features in the near-future. Better off building mainstream to skip HEDT platforms until you actually need one.