Canon and Nikon had traditionally offered two (1D / 1Ds, and D3 / D3x) for a long time until both of them merged the lineup, so it is not without precedent to offer two. That said, given how close the R1 is to the R3 in terms of market positioning, I can't see them continuing to manufacture the R3 once the R1 launches, so I think Canon will go back to a single integrated grip flagship body like Nikon.
I don't think Sony is going to offer an integrated grip in any camera now or in the future -- one of their "
5 fundamentals" for their cameras is "compactness", and adding an integrated grip runs counter to that.