UWP for Xbox, Mobile, and Desktop platform experience
While the proposal for a UWP app already exists, there are many features beyond replicating existing apps for new platforms that would make a UWP an extremely valuable part of the Mixer platform.
The premise of Mixer is to host shows, primarily video games but also more traditional shows, from the official Mixer show to the Windows Central podcast.
One of the most demanded features of traditional video platforms is offline downloads. Mixer could provide this feature through a UWP application for laptops, tablets, and phones. By using a timeout model where downloads expire after a certain amount of time disconnected, Mixer could download ads in conjunction with videos and allow even free users to enjoy a premier experience. While I personally would use this on mobile, the ability to watch VODs on planes or buses, etc., on laptops would greatly expand the reach of the platform.
The other feature that a UWP would enable is whole-experience home viewing. A UWP app could allow a desktop to cast a broadcast to an Xbox, and control the whole experience using their phone. With the expanding market of games (as well as the additional shows), you would expect Twitch and parent Amazon to nail the experience with Fire Remote and the Amazon Fire TV Twitch app. Since they didn't, it would be great to see you guys beat them to the punch. I personally would want to see the remote control, again, work on Windows 10 Mobile, but could understand if you skipped that platform. The Desktop and Xbox experience, however, I really want to see.