You mean deferred context? It's a complete failure. It needs too much CPU resource to work well. With a six core Sandy Bridge-E processor it is not a problem to dedicate five-seven threads for the driver, but most gamers just have two cores or four threads. With this configuration deferred context just slow down the execution in the critical scenarios, because the driver threads stole the resource from the engine threads. You may get slightly higher average frame-rate, but you will pay with much lower minimals, unless you have a top Sandy Bridge-E CPU.
The number one reason why Mantle born is D3D11 limits the game development. The problem is that a high-level graphics API force us a very bad programing model. I try to explain this simple. You write a code, and it may not work very well. You try to profile it to track down what is the problem, but the graphics driver is actually a limiting factor, because you can't see what happens in the driver. If you are lucky enough, you may find a solution in two weeks, but there is a huge chance that the problem is driver releated, and fixing that is may take one month or more. Now the tricky part is the code plus the driver may have more than one problem, so even if you fix one, than another will show up, and that's a another wasted month.
Mantle make this elegant. Actually this API is just executing shaders, and that's all. This will lead to a very good, console-style programing model, because what was in the driver in D3D, is now in the engine, so I perfectly see what's the problem with a code without any help (nV/Intel/AMD). And every problem is fixable with very little effort.