I think every reader of this site knows, or should know, rumors are just rumors. Hence, some or true, and some aren't. As I think I wrote before, I don't see the MP-E 65mm being upgraded, because this is a good lens (or, at least that's what I've read), and it has no competition. I think it unlikely Canon would upgrade such a lens.
As it takes a while to develop lenses (I think I've heard the figure 3 years mentioned before, I wouldn't know, and then rumors say some lenses get redesigned before release), rumors might be about lenses to be released over several years.