@A.Leon : For me Plex works fine pretty well. One remaining weakness is the flakiness of accessing files directly over SMB, but it has improved considerably. I don't recommend Plex's internal DVR support, as the interface just doesn't compare to Channels DVR, although it is a cheaper option. In fairness, some other users are less happy, e.g.:
I counted myself among them until recently, but some Shield updates have improved things no end. A critical component was poor removable drive support, but this has been largely fixed. Support of NAS drives is still extremely flaky, and mostly read-only. It's good enough for adding other collections to your Plex database for streaming, though.
AFAIK, Plex on the Shield support h.265 playback, but I don't know if there is any encoding support, although the graphics card could certainly handle assisting with that; Even if it were there, real-time might be a challenge, as h.265 encoding is notoriously resource intensive. h.264 encoding/transcoding/playback support is excellent, and it Direct Streams to Apple TV if you pre-transcode.
So far, and clearly it's been less than 2 days, Channels DVR hasn't be problematic at all for me, although as you'll see from above there might be some early (easy to fix, I suspect) commercial detection issues. It's very easy to just point Plex at the Channels DVR folders, and so far I haven't seen any failures to identify the right show/episode (again, limited experience).
I should probably add that there are always risks with cutting edge products, and the Shield is certainly unusual.
But I'm personally a pretty big fan, love the size, silence, low power draw, and sleekness. As added bonuses, their Shield-specific GeForce Now service (as opposed to the more open version which charges per GB) is extremely good value for occasional or binge gamers, and the inclusion of video services that the Apple TV does not provide (e.g. Amazon Prime and Vudu) makes it a nice supplement for TV viewing.