Unfocused let me try to answer those questions...
Firstly let me explain that I really have two quite 2 separate types of work, even though they can be a part of the same job.
1.) Structured. This is mostly film posters, magazine covers, or CD booklets. This is all shot at 100asa using a Hasselblad H series camera with a P65 back.
2.) Free form. This is mostly inside pages of magazines, CD covers, press & pr shoots, bands on stage, etc. I have used the EOS range for all of this since 1991, transitioning to digital for certain client with the D60, and all clients with the 1Ds Mkl.
So could one camera do both?
Yes, but honestly it would need to trump the pixel count of medium format to satisfy clients. They don't want to be driven in a Merc if the competition has a Rolls Royce, even though both will get you there just fine.
If Canon could put that 120MP chip in a fast body like the 1Ds, and have it work seamlessly with Capure One, which is the preferred software on most sets, then I think they would basicially kill the MF market stone dead overnight, much as the 5D Mkll did to the EOS. (I absolutely hate the Hasselblad H series camera, it was designed by people who don't work with cameras, and made by people who shouldn't make toilets. I loved my Contax 645, that was a lovely system, and I really regret it not transitioning to the 'now', however I'd be thrilled to be all EOS all the time.)
Do you really need the "bomb-proof" build quality of the flagship bodies?
That is an interesting question, I'd say yes because I like solid, well made things, but based on the sales figures that started this thread I'm in the minority of one! The 5D is easy to replace if you break it, and you can have three of them for the price of one EOS, so it has that going for it.
What features are deal-makers or deal breakers in a body? Frame-rate, autofocus points, autofocus speed, low-light sensitivity, micro-adjustment, articulating screen, continuous autofocus in movie mode?
They are all important factors in the current market, but I would certainly put image quality at the top of the list. If Nikon is giving you better images then you are doing your clients a disservice by working with a Canon. Quite honestly quality trumps everything, again that is why I spend so many days shooting with the P65, and now the Nikon D3s - they provide my clients with the best quality files.
If your only choices are the full frame 5D-type body or a more durable 1D body with 1.3 crop, which would you select?
I'd say the 5D, again because quality is king.
I also do agree with your opinions.
(I have a friend who works in satellite imaging systems, and they are already exceeding the quality of a 8x10 on a FF chip, so it is coming - eventually)
kubelik, you touch on something every notable, Canon in both braodcast and cinema make some of the finest lenses and equipment, and could well bring that qulity to our world if they thought they could make it profitable. I suspect that it would be hard based on the current cost of Canon's cine lenses... http://www.bhphotovideo.com/c/product/423758-REG/Canon_HJ11X4_7B_II_KLL_SC_HJ11x47BKLLSC_11x_2_3_Cine.html
As you can tell by the price above we are in an odd area where our market is really being defined the term 'pro-sumer' and these days that seems to be to the detrement of the 'pro', which is in part why I started the thread, to see what others would say, or want.