I am strongly of the opinion that Canon will not release any red-ringed EF-S lenses. I know neuro loves to whip out that image of the Powershot Pro1 but that was clearly a marketing mistake early on in the nebulous years of digital photography and a mistake that Canon has not perpetuated since then.
if the 1DsIII is Canon's flagship camera, and L glass is Canon's top-of-the-line glass, would it make any sense for someone to buy the 1DsIII and then discover there are L lenses that won't work on the camera? or aren't designed specifically for optimal utilization with that camera?
it'd be like paying for the highest level of VIP access to a fairly exclusive club, and then being told, "sorry, sir, you can't access these perks; they're reserved for our budget members." it just wouldn't make any sense from a marketability point of view, unless your goal is to lower the value of your luxury brand.
I agree with privatebydesign, there's nothing that precludes Canon from making a high-end EF-S line, but they will not/should not receive a red ring. Canon has shown in the past it will release green-ringed glass; there's no reason they can't come up with another color for premium EF-S lenses
I also want to question the perception that the reason L-designated EF-S lenses are inevitable because the APS-C market will dominate the future. I do think APS-C cams are around to stay, just like the 1/2.3" sensor and 1/1.6" sensors are probably around to stay. However, I think that FF cams will actually grow in popularity as time goes on, especially as Leica has already demonstrated how to stuff a FF sensor in a relatively small body. if you were to interview everyone who owns an APS-C cam, I think a very large number of them aspire to own a FF camera someday; knowing that there is a difference in image quality, and you are utilizing your wide angle lenses to their full capability. I don't think canon should dilute its luxury brand in the long term for short tem profit.