This is the first time you're hearing about this?? o.O Its been posted on Phoronix quite a few times.
The reason you can't have multiple drivers installed right now is because they have to provide libgl.so and they all conflict. So the new plan is to make libgl.so be a sort of launcher that loads the correct vendor-specific library, this way they can all co-exist on the same system. Right now the only way I know of that you could have Optimus working (which requires Intel drivers AND Nvidia drivers, but Nvidia replaces tons of Mesa stuff) is for the Nvidia driver to internally provide the Intel driver.
Once the new ABI is defined and set, multiple libgl's can exist together and be loaded as needed