The IEEE The 40G and 100G Optical Ethernet Task Force recently revised their PAR and 5C documents which are going to 802.3 for approval and then EC approval. The group added EEE capability.
"The closer a Physical Layer technology comes to the Shannon Capacity of its channel, the less likely Moore's Law is going to help it achieve market success."
Originally coined to justify the "Short Reach Mode" for 10GBASE-T, this has been proven out and provides some useful guidance for future technology discussion as we consider things like 40GBASE-T or even future fiber-optic solutions where the electro-optical interfaces become the dominant challenge.
Considering shielding for higher speeds is also important to keep away from Mr. Shannon's limitation on SNR.