We may all be disappointed but I already booked my trip to Photokina just in case. According to all the speculations, there seems to be a few very straightforward scenarios:
1 - Photokina yields nothing (or just an N version with a larger screen). Canon, as everybody else, is working on next generation sensors and won't be ready to show anything until later next year. Doesn't sound very likely as all the others are trying hard to catch up and will come up with new stuff.
2 - We get a completely updated camera, smaller, with a modern interface, different battery, very high frame rate, larger pixel count etc.. Not impossible and most people expect just that. Tentative specs would be 20+MP (just because they can), 6 to 8 FPS (because that would be very useful and cancel the need for a separate 1D line), 5D-like interface (because the 1D interface is unnecessarily complex and because with Canon, ergonomic advances tend to trickle from medium range upwards) with 1D-like Build, AF and Metering (no need to change something that works). Could be made significantly smaller by using Li-Ion batteries. Again, possible but not so likely.
3 - We get halfways with an N type update and a new sensor but not much else. This is my personal favorite because it asks for the least effort from Canon. The advance in quality the 5D brought shames the old 16.7MP sensor so it seems urgent to bring it up to par. For marketing reasons, it would be necessary to increase the number of pixels so customers can be persuaded to trade up. Making the rest of the camera conform to 1D MkII N specifications is just a matter of picking parts in the common bin. The "magic" 22MP everybody has been mentioning is not that silly as it allows you to take your picture, crop a good chunk off it (necessary for layout even if the framing was perfect) and still print at optimum resolution on a double page spread, the publishing standard. So quite likely. Although it would make sense to make it as fast as possible to be able to get rid of the 1D, I am not sure it is technically possible now with that many pixels.
A playable joker would be the introduction of a 3D to complete the range (12MP 5D, 16MP 3D, 22MP 1D) and fill the gap left by the 1D Mk II in the price hierarchy if it is discontinued. If it is not, it probably deserves to be upgraded to 12MP.
I expect that Canon will be concentrating most of its efforts at Photokina on its new line of IPF printers with a 6000 and 7000/8000 joining the 5000 and 9000. They were not properly demonstrated in the previous photographic shows and need a good public introduction. The fact that Canon downplayed the photographic prowess of their previous large format printers for several years waiting for the IPF to come out probably means it's an important long term strategical device for them to which they will want to give its due soon.