Some drivers for 3D shutter glasses on CRT monitors used that same mode as brainwarp.
I tried it and it was working, and was more logical, because the display was already alternating between left and right eye anyway.
I tried Day Of Defeat with it, so they found a way to hack the game engines with a driver similar to what Nvidia 3D vision does.
But there were issues.
The first issue was that a lost of sync and an inversion of the eyes, as the CRT or glasses couldn't know wich frame was left or right.
The second issue was frame dropping, and the fact that when you drop a frame you can display a black frame, or display the previous one, which would mean going back in time, as the eyes are always display T+1.
So you are right in saying it's a gimmick, because it means also the engine would need to render at 180fps, even if the GPU doesn't compute more frames, that's a lot of strain.