I don't know about those rumours but simple logic says that the EOS 1Ds Mk II is due replacing since it's nearly been five years since it's release.
Something in the realm of 20 ~ 25MP as far as pixel density goes is certainly within the ballpark and eminently workable. I know that Nikon is working on a FF dSLR with a pixel density of ~ 24MP, so it looks like both Nikon and Canon are really gunning for the pro end of the wedding, portrait, advertising and studio shooter markets, since those pixel counts are encroaching on medium format territory... and not everyone can afford or justify those juicy 22MP+ digital backs
What I can say with certainty is that you're looking at a top-line ISO of 1600 for such cameras, with anything over and above that value existing as a 'boost' option. Photosite density has a direct correlation to ISO noise for any given value and is unavoidable... the only way to negate it is with in-camera ASIC processing to account for that noise.
Anyways, it certainly points towards interesting times ahead; I just hope that Nikon's FF dSLR doesn't cost me an arm, leg or kidney