There was footage of a version of Windows 10 running on the Elite X3 that utilized cshell and coreOS elements I believe, this from Zac Bowden.
At the moment the 950 xl is the only device capable yet powerful enough to run a version of full Windows 10. Developers are able to unlock the boot loader for that device, first off which is the only way to begin trying to install a new separate operating system then that which is installed (Windows 10 Mobile). Windows 10 ARM is able to boot and run on the 950 xl. It is the closest thing to full windows 10 on a mobile phone as you can get. It's in development so certain elements dont even work at all, like cellular and maybe wifi. There is no known way to boot loader unlock the HP Elite x3. Hope you did not buy it expecting it to be that easy or even that way.