A long long time ago, there was work done on ARB_Sync, and it was good.
But then the promises started, it was going to be in 3.0, there was just some work to be done, etc, etc.
In the end, no ARB_Sync, NVidia and Apple have somewhat limited extensions that do some of it, ATI has none.
This is a huge hole in OpenGL for some applications, specifically where it is critical to avoid CPU busy waiting while still maintaining low total system latency.
Is there a reason that ARB_Sync died its death? Can it come back from the dead? I think it would be a significant enhancement these days.
As an indicator, our application gains 30-70% total performance on NVidia cards by using NV_Fence, ARB_Sync should allow us to gain even more. It would also seem to fit in nicely with the general direction of both GPUs and software developers expectations.