According to a rumor posted on CR, the 1D Mark V will be here in late 2011 or early 2012, and will be moving into 1Ds territory as the new high-end DSLR.
Presumably that means higher resolution (and a CR states, probably Full Frame). The needs for a studio camera and sports camera are very different, so sacrificing speed (frame rate, high ISO abilities, super-fast autofocus) for resolution doesn't make sense, but then we are also hearing vague rumors that the 1Ds line is going to be a 'radical departure', so this could fit in with a new product strategy from Canon at the high end.
The other major item that will impact the Mk V (both spec's and timing), is that Nikon is expected to release the D4 this summer. The Mk IV didn't exactly blow the Nikon D3s out of the water, and with Nikon expected to take a large step forward with the D4, the Mk V needs to be something special.
Source: CR on 1/12/2011.