Optical design of the 300mm f/2.8 FE
An area were Full Frame Mirrorless systems still lag behind their DSLR competition is the telephoto lens offerings. Sigma is now actively working to fill the gap and patented this new Sigma 300mm f/2.8 for mirrorless system cameras (which definitely means there will be an E and L-mount version).
Here are the lens specs. CL means the 300mm lens with 1.4x teleconverter attached: