This doesn't surprise me at all, as the world economy continues to turn around and disposable income goes up Canon needs sales to fund R&D for the next generation. The 1Ds has never sold in great numbers and releasing a new $6 - $8K body that will NOT sell in great numbers probably doesn't make financial sense right now. Releasing a high performance, FF body would provide entry into a market where Canon isn't currently competing. The 1DIV comes at too high of a price point and competes with more expensive Nikon bodies so there is room here for another body to gain some market share.
I think we just might see the mythical 3D finally released to fill this niche with the 5DIII taking on the high MP "studio" duties until the next 1Ds is ready. I believe Canon wants the 1DsIV to crash the MF party where people are willing to pay a lot more for the ultimate in IQ. The 3D has been talked about for years, but it makes sense to release it now as it would complete Canon's advanced amateur, semi-pro lineup very nicely. 7D high performance crop, 5D ultimate FF IQ for studio work, 3D fast & FF 16-18MP for the "all of the above" shooters like myself. Canon would literally have something for everyone who wants to step up from the Rebels and upgrade their aging XXD cameras, many of these people myself included are considering the dark side because it seems that Canon wants us to buy 2 cameras to shoot everything we like. I still don't know what purpose the 60D serves, it seems to exist only to fill the price gap between the T2i and 7D.
The 1 series remains the ultimate workhorse with the best weather sealing, fastest FPS, best AF and great IQ, but also a niche camera.
Of course this is all wild speculation on my part, but it would allow Canon to compete on every front. People disagree with me but I'll bet Canon execs get a little heartburn every time they hear about the D700 and it's replacement, its a market they could have been dominating for years....