On September 4th, Special K just added it to the latest developer build (only downloadable via the Special K Discord server).
If you can't click on that, accept this server invite to Special K Discord Server before clicking the above image.
I should also add that Kaldaien was happy to use of my Blur Busters research to figure out how to add support for this -- inspired by Tearline Jedi research that Blur Busters did which also inspired Guru3D to do RTSS Scanline Sync too.
Short of VRR, this is one of the lowest-latency tearingless methods of sync technologies (tearingless VSYNC OFF -- essentially emulates an ultra-low-lag version of VSYNC ON via raster scanline-based tearline hiding techniques with VSYNC OFF).
