One of the components (not yet finalized) of ATSC 3.0 is an entire web browser that runs as an overlay in front of the video [1]. Which itself supports LocalStorage, XHR, and all the goodies you've come to expect - and EME DRM, of course.

[1] http://www.atsc.org/wp-content/uploads/2016/12/A344S34-230r1...