Canon is working on a new 100-400mm lens that will replace the current EF 100-400 f/4.5-5.6L. Many of the future Canon lenses will come with a Diffractive Optics DO element (see previously filed patents):
“A new 400mm supertele is just the beginning. Canon also says it plans a replacement for its 100-400mm zoom and new compact models using diffractive optics.” (via Cnet)
Here is some more information on Diffractive Optics (DO) from Canon USA: