What? I mean what? What on earth does the release timings of updates to webkit have to do with the Xbox...microsoft doesn't even use webkit in anything it builds. Thanks for the info on html 5 for ui I guess but your whole post is just a big non sequitor.
Sony, AMD, Microsoft and maybe others are jointly releasing UHD and UHD Blu-ray as well as Vidipath. The SDK Comcast and others are using for Vidipath is Gnome Mobile Initiative Webkit and the APIs Sony uses are based on Gnome mobile. Same for Samsung's Tizen and Google using blink.
The common DRM for Vidipath is Microsoft's Playready, WMDRM and Playready ND. Microsoft's UI and browser is based on WebGL and Webkit HTML5
compatibility because all UHD Media including Vidipath uses HTML5.
ATSC 3 is the UHD Antenna TV standard which is supposed to reach candidate status Q1 2017 and any changes to it will be reflected into every other UHD delivery scheme and HTML5 as well as vice versa.
Vidipath Cable TV DVRs are already available, Antenna TV ATSC 1 & 3 Vidipath tuners with optional DVR should be shipping early 2017. UHD Blu-ray with digital bridge and optional DVR Vidpath servers are the third part of the coming in home media sharing with Vidipath.