The 1D IV has only been around for about a year and a half. Why would Canon be replacing that fantastic camera already? There are people out there who like its crop believe it or not. It's ideal for many big telephoto users. If Canon is coming out with a Mark V that has full frame for a lot more money, I will happily pass on it. The current Mark IV is just about perfect to me. There is apparently a lot of whining on the internet for a fast full frame camera. I do hope Canon comes out with one so they can be happy.
Canon will produce a fast, FF body because Canon's number 1 competitor already offers multiple, fast, full frame bodies. If a crop mode is offered, the big telephoto users will still have their crop factor while allowing the ability to go ultra wide when necessary, something alot of APS-H users complain about. If we finally get this kind of body, other than the price which is also a matter of speculation, everyone wins.
I shoot everything from landscapes to sporting events, this would be the ultimate camera for myself and thousands of others, I'm glad you're happy with the 1DIV, it means 1 less person competing for what will surely be limited stock if this turns out to be real.