It would appear that Nikon has a 50 f/1.2 in the works.
http://nikonrumors.com/2011/06/22/nikon-patents-update-3.aspx/
I'd be curious to know how much of an obstacle patents pose to competing manufacturers. I mean, why register a patent if it doesn't create an obstacle for other companies? Thus, if Canon is first to get patents on the logical "next step" for f/1.2 technology, it would make sense that Nikon might have trouble developing an alternate configuration, or a variation that doesn't violate the patent.