Variable refresh rate technologies are getting standardized as VESA Adaptive-Sync, HDMI 2.1 VRR, FreeSync, in addition to G-SYNC. Microsoft’s Scorpio Project (the next XBox) is already planned to support variable refresh rate.
Mark of Blur Busters is now an Invited Expert in the W3C Web Platform Working Group.
We currently have github #375 on W3C’s HTML issue-tracking system to add VRR support and VSYNC OFF support to HTML 5.2.
Since web browsers will eventually need to gain VRR support, the HTML 5.2 standard will need to gain preliminary VRR / VSYNC support.