The 5DX has been mentioned before, and if you think about it, it makes a lot of sense.
It provides an upgrade path for 7D and 5D2 users in a single stroke, giving all a bit of everything.
As has been pointed out, it will drive sales for more expensive L lenses, it will simplify the production process (1 line instead of 2), and it would sure as hell give Nikon and Sony something to think about.
The battery grip with the extra joystick makes it almost worth upgrading just for that feature alone.
So, for your £2500, the 22mp FF is nothing new, which means Canon have to introduce something to make it worth while upgrading to.
So, if we're talking about a 5DX, what would i expect?
Well if we take the 22mp FF as the sensor option we then have to consider something that makes it worth upgrading for.
First off, the AF has to be a given - it is the only issue that has ever received negative press on the 5D2 (apart from the initial black dot thing). And there is no way 7D'ers would upgrade to this unless it had at least 7D focusing - so that or a pro series AF seems most likely. Would it be a 1DX AF? I can see pluses and minuses for this. Would be cheaper to implement production wise - but would it detract from 1DX sales?
Jury's out on that - but it would certainly get the 7D folk chomping at the bit.
ISO - up it to 12800 or 25600 working, again, 5D2's would be happy with an extra stop, and the 7D brigade would be happy as well.
Dynamic Range - either/ or - could be one of those things they leave for the 1DX.
Weather proofing - by having the small body format, it means the battery grip is an add on, which will always compromise weather proofing. I would not expect this to be as good as a 1DX.
Buffer & Frame Rate - both severely hampered in comparison to the 1DX. You gets what you pay for...
Dual Card Slots - i suspect this might be slipped in to aid the video brigade (for those who can't afford a 1DX) - remember it only allows extended video length, not improves video quality to 1DX level. It would also be one of those clinching features for those who are umming and ahhring. As for low end wedding togs, what a boost.
GPS built in - this is a gimmick that would appeal to the traveler and landscape brigade more than sports brigade - though the wildlife lot might not complain. I say gimmick - i am well aware of its uses - but i still do not see it as a real marketing issue for most because when importing pics, the location tends to end up in the tags and keywords for ease of search.
Shutter life - held at 150k or 200k - which would make you wonder whether to stump up now for a 1DX and get that 400k shutter life, or get in half price increments!
Oh, and finally, that wonderful battery grip with the additional joystick. Whilst an optional extra, i wonder how many wedding and wildlife togs would get such a battery grip, who previously haven't bought one? The ability to swap from landscape to portrait and select focus point on the fly would be an absolute must - but you're only getting this wonderful 1DX feature at a premium (£300) which in turn means more revenue for Canon and means you're getting closer to the 1DX price tag in steps.
Yes, the 5DX would definitely be for people who can't afford a 1DX, but would like one. £2500 for the body, £300 for battery grip - that's almost £3000 for a stripped down 1DX that may well have a street price of £4200 after initial launch. It's good enough to make people stretch, but short enough in features to make the pros (people whose living depends on getting 'that' shot) needing to cough up the extra.
Most importantly - it is a strong enough feature set to get the 'newcomers' choosing Canon over Nikon and Sony.
I may be totally wrong, but it would follow on with Canons 1DX strategy and would certainly leave Nikon playing catch up. I know a few Nikon shooters who do not want a 36mp D800 and would swap to a 5D3 if it held to the 21/22mp region.