I'm looking for a solution that offers 4K 60Hz with 10-bit colour gamut support and Nvidia doesn't look like it will support that anytime soon.
It does with the Shield TV, and that's probably your best option for true 4K 60Hz 10bit playback.
If it's just HEVC 10bit decoding you need, then go ODROID C2/Wetek Hub/Play 2 etc, forget Intel NUC's and x64 PC hardware for the moment IMHO.