Umm, hello. We had the radical departure. It's called the 5D2. That happened 2 and change years ago. What have you done for us lately Canon? Not much. 5D2 remains a slow machine. 1Ds nowhere to be found. 1D4 is not the D we're looking for.
So what if the replacement for the 1Ds series is a 5D3? I don't give a horses arse what they call it. I don't care if it replaces something, doesn't replace something, is a bridge to nowhere, just build a better responding machine around a full frame sensor that works with the EF mount. I'll either keep my 5D2 as backup or swap it for a 7D backup.
What Canon should do but won't (note my marketing nomenclature proposal ditches the "D" for digital shtick since we obviously know these are all digital camera, and replaces it with the lens mount type built exclusively for it).
1 M = medium format sensor, 4 fps, beyond insane DR, modular, new M mount, yada yada expensive
3 EF = 30+ full frame sensor, 7 fps (boost to 10 with some grip thing), wicked AF, high iso, low noise, insane DR
5 EF = 30+ full frame sensor, 5 fps, medium sick AF, high iso, low noise, insane DR
7 S = 21 mpx APS-C sensor, 8 fps, wicked AF, improved DR
xxS = whatever profitable rebel line they want to keep milking
9ml = ??, new ml mount (adapter for old aps-c legacy lenses)
11ml = ??, new ml mount (adapter for old aps-c legacy lenses)