The title is misleading: Nvidia is doing NOTHING to port Optimus to Linux - it's the opposite: Xorg developers are working to make it possible for a GPU to offload tasks to another GPU on Linux (and any system that ports the Direct Rendering Manager 2) without going through a proprietary interface: instead, any driver that implements RandR1.4 can be used to offload rendering tasks, making combos such as an AMD card displaying on 6 screens using an Nvidia card to generate the 3D on them a possibility, or an Nvidia Tegra using any integrated chip to render, say, a video, or, as in the present case, an Intel IGP using an Nvidia chip to render the 3D content.
And, as indicated, since the interface is open and shared across all GPU makers (RandR1.4), stuff like Nvidia disabling PhysX on systems using an AMD card cannot happen... Or at least, can be thwarted.