I had it wrong... neither Shield nor HiMedia Q5/Q10 Pro will play 4:2:2 and 4:4:4 HEVC.
Now I see why @wesk05 was asking if I was sure HiMedia actually played his 4:2:2 and 4:4:4 HEVC clips. Continuing to find that playback needs to be validated in more ways than one I tell ya...
I tried again w/HiMedia Q5 Pro, and what actually happens is that it tries (and fails) to play HEVC YCbCr (YUV) 4:2:2, then 4:4:4, and automatically goes to the next file in the directory... which happens to be 4:2:0 the way I have my filenames named:
The 4:2:0 clip does play, and it was what I was mistaking for 4:2:2 and 4:4:4 playback. Damn! Uncovered this when I remote-connected to the player via my PC and ran a diagnostic tool (available on Futeko forum) to verify while playback was happening. It was indeed playing the 4:2:0 file. I had initially thought given the difficulty in rendering 4:2:2 and 4:4:4, HiMedia was just taking longer than usual to initiate playback.
So, with Shield, HEVC 4:2:2 and 4:4:4 both result in green-pixellated mess, with only HEVC 4:2:0 playing okay. With HiMedia, it won't even play HEVC 4:2:2 and 4:4:4 at all, and like Shield, HEVC 4:2:0 is okay.
As for 4K playback differences between Shield and HiMedia Q5/Q10 Pro, the more I test, I'm not finding any significant differences, with both performing as well, very similarly.
Neither Shield nor HiMedia can play 4:2:2 MPEG2 either, not w/o serious artifacts. I've only found i3/i5 NUC and Sigma-based media players able to play this. H.264 4:2:2, I don't have samples to test with.