Reddit user “OomaThurman” has figured out how to improve the video quality of the Xbox One to PC game streaming function in Windows 10. You can view the instuctions how at the above link – just remember we take no responsibility for you monkeying around in your PC's config files. We did however take the responsible step of verifying the information ourselves and found that the stream quality is noticably improved though can hit around 15-20mbps when actually playing and did cause issues with a wireless connection, wired was fine thouugh so you'd better have a wired connection to your Xbox if you want to take full advantage of the improved quality.

"Simply edit the userconsoledata in the xbox app folder and change IsInternalPreview to true. C:\Users\%USERNAME%\AppData\Local\Packages\Microsoft.XboxApp_~~~~~~\LocalState"