While I generally like the idea to use native players (since we get app support for Plex extremely quickly), it's been shown (successfully) that developing your own video player will immensely enhance the playability of movies and TV shows on the Apple TV 4.
I think focusing the development for the Apple TV app to use it's own video player we would be able to get Direct Play playback for DTS/Dolby, subtitles, and high frame rate videos. With the current native player on the Apple TV this isn't possible, but a player developed for the Apple TV can be built that will play all of these files extremely well.
I understand it could take a little while to do, but I think the quality of the product would be enhanced drastically.