Canon applied for a patent on a 70-300mm f/4-5.6 lens in March 2011. Presumably, this is an update to the consumer grade line of 75-300mm non-stabilized lenses.
As with all patent applications, it’s no sure thing that a given invention will make it market; however, lens patents seem to have a better track record of predicting future products than other things like fuel cells in DSLRs.
You can check out the full patent PDF here.
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