[Milhouse]

are your builds capable of doing 4k HDR 10bit file playback on my setup

No, there is no support for 4K HDR 10bit.

First of all, Kodi doesn't support HDR (yet).

Secondly, VDPAU (the hardware acceleration used by Nvidia GPUs) doesn't support 10bit HEVC (I assume you mean HEVC and not H264 as there is no hardware acceleration at all for H264 10bit).

4K 10bit HEVC support is possible with these builds, but currently only on Intel Apollo Lake/Kaby Lake hardware.

Also, the wiki has recently been updated: http://kodi.wiki/view/Supported_hardware#Desktop

or are they mainly aimed at Intel graphics

These builds are not explicitly aimed at Intel (we - and Kodi - support AMD too, as well as Nvidia) however the underlying video hardware acceleration library favoured by Kodi developers on Linux is called VAAPI and this is supported by Intel hardware so this is where most of the development is.

The library used by AMD and Nvidia hardware is called VDPAU which is stagnating and will most likely die in future, along with Nvidia hardware support (AMD also supports VAAPI, and this is the route for AMD hardware in future, once the necessary changes are made in Kodi).

do you or anybody else reading this have any idea of a build that might suit my setup or if there is even a rough timescale to when Libreelec will be able to do 4k HDR playback?

No such build exists, and I honestly couldn't tell you when 4K HDR support will happen - end of the year would be my best guess (around kernel 4.13.y/4.14.y), and this assumes support in various parts of the stack including Kodi. And whether VDPAU will have the necessary support... no clue, but seems unlikely.

(Maybe I'm going out on a limb here, but if it's not obvious from the above: Nvidia hardware is not a good long-term choice for Kodi on Linux)