4K is already here, in the form of the GH4 for DSLR type cameras, and the AX100 for camcorders. If products like that are going to "cannibalize 1DC and C500 sales" (not going to happen btw), then by not having competitive products Canon will be surrendering that market share to Panasonic and Canon.
Odd thing is, both Sony and Panasonic have high end professional products as well, why are they not concerned with going to "cannibalize bla and bla sales"? Answer, because it is a different market. There will be no cannibalization going on, only ceding of market share.