You can already have a 720p video stream !
There is the SetVideoResolution command, which allows you to toggle between the "normal" 1080p recording + 480p streaming, and a 720p recording + 720p streaming mode.
The encoder can not handle one 1080p record + a 720p stream at the same time, so increasing the streaming resolution has to reduce the record resolution.
Please note that the "streamed" 720p il still at a lower quality (both in h.264 profile and bandwidth) than the recorded one, but it will be better than the 480p
FYI, this mode is enabled by FreeFlight when using the Cockpit Glasses, to improve the FPV experience.