Well, you shouldn't be surprised that you don't know because...
Anyway, from the Rampage V Extreme right down to the lowly ASRock boards.
Not blaming motherboard vendors as this is a communications fail between INTEL, board vendors and memory providers
Simply put, X.M.P is largely broken if not completely broken on all boards. Memory vendors can and do make memory that complies with X.M.P 2.0 and INTEL does validate it, however they only validate the profile not actual operation. So lo and behold you buy shiny new memory, load X.M.P and it doesn't work. Some boards are limited to 2,666MHz DDR4, others 3,200MHz and some 2,800MHz.
I would like to say this is something BIOS updates can fix but it isn't so. What you don't know is that prior to X99, motherboard vendors didn't have memory to test with, memory vendors didn't have motherboards. they can't commit to a production run because there's no memory. The endless cycle. INTEL does provide development boards, however this time it was server boards they provided, so as a motherboard vendor you must essentially work from a Server platform to make a channel\retail board. The speeds validated for the server platform are well, 1600MHz to eventually 3,200MHz. That doesn't mean much if anything at all, because INTEL only stipulates support for 1600 to 2133MHz memory, the dividers for higher memory frequencies are there, but that's pretty much it.
What you'll see is some new boards showing up almost out of the blue. These fix the initial design issues that plagued all boards.
Examples of the new series of fixed* boards are the GIGABYTE Champion series and the single ASUS Sabertooth X99 TUF. Believe it or not the TUF is a better overclocker than the Rampage V Extreme and it'll hit higher everything essentially, including having the ability to run 3400MHz memory out the box, which the RVE and others cannot (save for Champion series).
If you don't care about high speed memory though this won't matter, all boards work fine with 2,400 to 2,666MHz DIMMS.
Behind all the big monies, massive buildings, R&D budgets and technology you can't put wrap your mind around. Thousands of people and millions of man hours, it is just still regular folk like you and I. Since no person is impervious to oversight, no organization is either. It is unfortunate but it is the truth. It is not intentional, but believe it or not the situation was even worse with X79. Hence it was revised mid-life and nobody was the wiser. (PCIe 3.0 support was improved/added). That's how the Rampage IV Black Edition came about, it was a new ME code and all the updates for platform. Some motherboards were technically abandoned on the X79 platform and they could hardly operate at default settings.
Since HEDT are not volume platforms hardly any vendor bothers with investments in them. The odd thing here is that, many of the problems (not mechanical ones but BIOS related) can be fixed within a week with just sitting down and having all the resources poured into them, but it doesn't work like that with technical departments.
Is there no fix for the boards out there already via a BIOS update? XMP would not enable in the BIOS on a Asus X99-E WS even with the switch on the board set to enabled.
That's exactly it. They actually can't be fixed and even if they could. They would not be. Once again you can blame websites for this, because they don't actually test boards as so much as stare at them and write reviews.
It's on so many more boards in the wild you'd not believe it. If the journos don't tell the truth and keep handing out awards, then that sends a message of approval to the vendor techies, thus if you have a problem, you're an isolated case, not a symptom of a real problem.
So can you take motherboard manufacturers to task? You can't really simply because:
1. Your CPU is only certified to operate at 1600 to 2133MHz as per INTEL spec, which it does.
2. The motherboard only stated it supports memory speeds x,y,z via OC and there's a disclaimer about OC claims.
3. What you can do though is call out BS reviews for what they are and make journos account for them. Not aggressively but asking simple things like why is it an entire review of an overclocking motherboard only has CPU overclocking via multiplier and CPU voltage? That tells you nothing about anything. What really matters with X99 is how well X.M.P works, memory tuning, and Uncore. Everything else is entirely CPU sample dependent.