I'm curious as to why you think FF is not so important for landscape. I would have thought the opposite, though given the quality - or lack of - of my landscapes, I'm prepared to listen to other views.
This topic has been discussed at lenght already. A poster called Didger did also conduct in depth analysis between his 1Ds and D2x and his conclusions were identical to mine. He did unfortunately pass away a few months ago in a tragic backcountry accident.
Using currently availalbe cameras, the question ends up being which of the D2x or the 1Ds2 is the better tool for landscape applications (the 5D will IMHO not change the game too much - see below). As I said, I am not trying to convince anyone, and I know that amazing pics can be taken with a 1Ds2. No doubt.
From my selfish standpoint though, here is why I feel the D2x to be the better tool for landscape applications:
1. More DOF, which is key for landscape as my experience with 4*5 has painfully taught me,
2. The image quality is overall very similar, at least up to 400 ISO (which is all I need for landscape):
2.1. The DX wide lenses provide a very uniform image accross the frame, down to 12 mm on the 12-24 mm. This appears not to be the case with the best L lenses on the 1Ds2. Pom is right to say that Canon will probably release better wide zooms, but they have been very slow doing so (the 1Ds was released 3 years ago), and those will be expensive new lenses which will pretty much cancel out the supposed advantage of being able to use one's existing set of lenses.
2.2. The colors delivered by the D2x are great,
3. The D2x is much lighter as a system:
1. Body is 200 gr lighter,
2. Battery life is longer and batteries are nearly twice lighter (180 gr vs 335 gr).
-> For an intensive 5 days shooting in the wild, where 3 or 4 batteries would typically be needed with a D2x (against 4 or 5 with a 1Ds2), this results in at least 1 kg less weight to carry around with the D2x. A BIG factor if you actually trek in the high country.
I can already hear some people saying that 1 kg is not a big deal... it is for me.
If you factor in the fact that DX wide are also lighter, then you end up finding out that you can actually take one more long lens like the 70-200 with you for free weightwise compared to a 1Ds2 based system... or a light Goretex tent for instance (mine weighting only 1300 gr).
The gap weightwise does of course further increase if you take a second body along,
4. The ergonomics of the D2X are great which helps shooting with gloves in the cold for instance (something I do during the winter months in Japan). 2 great additional features are the display of the ISO value in the viewfinder together with WB value,
5. The D2x is much cheaper than the 1Ds2. The 5D will change this, but I don't think that I would trust an important shoot in the wild to a 5D class body though. All those that have been writing reviews about how rugged the 1Ds2 is, and how important this rudgness is for landscape shooting should agree with me on this.
6. The day I start wildlife, the 200-400 f4 VR (behaving like a 300-600 f4 VR on the D2x) will be available a provide a much lighter, cheaper and flexible alternative compared to the 500f4 and 600f4 1ds2 users would have to carry along. Again, not a problem if you shoot from the car, more so if you actually trek to location.
7. Best in class low light AF. Great for pre-dawn shots where it is too dark for focus manually in an accurate fashion.
As a Nikon user with an existing set of lenses, it is really a clear cut choice...
The 1Ds2 probably has some advantage over the D2x though:
- more tilt lenses -> I hope that Nikon will provide a solution to this,
- a wider viewfinder,
- better high ISO image quality, not a factor for landscape, but a bit more so for wildlife (which I haven't been doing too much),
- possibly a bit more DR, but this isn't that clear.
But those are IMHO far from outweighting the other advantages I see to the current Nikon system.