[noggin]

X86_64 inc. AMD - Windows only - HDR10 support -->> see Kodi DSPlayer – DirectShow Player for Windows thread (click) for current status.
Not a Plug n Play solution. Unsure if that combo does auto colorspace switching or you have to manually fiddle around all the time.

I may be wrong - but I don't think Windows currently does EOTF switching, let alone colour gamut switching? I think that you select HDR10 EOTF (i.e. ST.2084 PQ) output at the OS level - then everything is output in HDR10? (With SDR Rec 709, and Rec 2020?, mapped into a Rec 2020 HDR10 output?) nVidia had SDR/HDR switching which pre-dated official MS HDR support, but now that MS has an HDR approach (i.e. on or off at OS level) then I think this may be deprecated?

NVIDIA Shield - will be OK for 4K HDR10 only, but some demanding users report issues with washed out color output when viewing regular SDR content on various 4K HDR displays. Unless you manually fiddle with Android OS display settings all the time for mixed SDR / 4K HDR usage.

Yes - it appears that this is a display/Shield interaction issue on TVs that don't do what is expected when fed SDR Rec 2020 content (as the Shield TV will map SDR Rec 709 into SDR Rec 2020 colour space) With the latest firmware the Shield is following the correct standards recommendations for mapping SDR 709 into SDR 2020 according to @wesk05, but some displays don't handle SDR 2020 as per the standards?

In theory there is no reason why permanent Rec 2020 colour gamut output should be an issue, but if you have a TV that doesn't follow specs as expected this is probably not a consolation.

Make sure you can return the device if you cannot put up with such ongoing issues, any fix will NOT come from NVIDIA that quickly.
See Post #1 of this thread that has all the links discussing such Shield issues.

Isn't this a display issue, not nVidia's, to fix? Or are you suggesting that nVidia introduce Rec 709/Rec 2020 gamut switching? Not sure that will happen - they've obviously decided on a fixed colour gamut output approach. (Or Android/Google have)

Both combo's are the ones to consider if you use really demanding graphically intensive Skins like Aeon Madnox, due to the powerful GPU's in such devices that can draw graphic user interfaces really quickly.

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AMLogic S905D or S912 devices (Gigabit ethernet / 1000M only devices for 4K HDR & Atmos):

DIY S912 devices will be the fastest when running LibreELEC Krypton or CoreELEC Leia - but LE / CE (Linux) Kodi support may finish at Kodi Leia due GPU drivers used.
Great bang for the buck - suggested combo - something like THIS (click) or a MINIX U9 (A2 lite remote is highly recommended - works with everything)
There is good Open Source coding work happening to write compatible Linux GPU drivers for such S912 devices - so who knows what will eventuate by this time next year for Kodi v19 M use.

Otherwise consider the S905D devices like the really well supported Vero 4K+ or the DIY MECOOL Ki Pro, those will have a longer term Kodi future.
Read the Vero4K+ support forums for any current issues.

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Don't need Bluray Atmos audio and want to dip your toe in 4K HDR -->> the cheap - 2018 Amazon Fire TV Stick 4K with a USB3 > Gigabit Ethernet adapter
OR

Yep - but not without issues when handling anything interlaced, particularly H264 Live TV or 1080i Blu-ray rips. It's very early days with the Fire TV Stick 4K.

Really the easiest 4K HDR (no Bluray Atmos) - Plug n Play solution of the entire lot with really only minor issues -->> the Apple TV 4K.

W. 

  
Yep - though the ATV 4K currently only runs MrMC - which is a fork of Kodi Krypton, modified to gain App Store approval from Apple. There are ways of sideloading full Kodi but they are non-trivial.

The ATV4K is fantastic for Netflix and Amazon Prime, and many other Catch Up TV apps. Personally I prefer it toe the Shield TV for these applications due to dynamic frame-rate switching being supported properly by the apps on this platform. I don't recommend it for Kodi, simply because it doesn't really run Kodi. (Have the HDR10 metadata pass through issues been fixed on it now? ISTR that there was a permanent fixed metadata output on HDR10 content from MrMC that could mean tonemapping - to cope with HDR highlights outside your display's capabilities - could be compromised?)