According to a post by Valerie Maguire on Siemon's Network Infrastructure Blog, the Institute of Electrical and Electronics Engineers (IEEE) has formed a study group to investigate lower-power, lower-cost, higher-density 100-Gbit/sec Ethernet interfaces for optical fiber.
The post says that for multimode fiber, the study group will investigate reducing the number of fibers from 20 to 8 per channel; reducing the power consumption of transceivers; specifying a narrow form-factor array multimode interface; and reach on OM3 and OM4 fiber. For singlemode fiber, the study group will investigate adopting higher lane speeds to reduce the number of wave-division multiplexed lanes; reducing transceiver power consumption; specifying a narrow form-factor duplex singlemode inteface, and reach on OS1 fiber.
From the Network Infrastructure Blog, you can link to the IEEE 802.3 call-for-interest presentation.