a) I would say that Canon will go full frame only for the future, unles any of you mroe experienced people know a reason why they would not. I mean after economies ofe scale kick in, which they are already, the price diffrence between a full and medium sensor will be negligible I would think.
Why not just use the Canon lenses at a 1.6 crop? What's wrong with that? If the problem is that you want a sider lens, you could buy the wise that only fits teh 1.6 crop. I don't know what you mean when you say "lack of fast top quality lenses for the 1.6" when I'm using a 70-200 L f 2.8 IIS
On point (a), I have already stated often my reasons for being very skeptical about those huge 24x36mm sensors every being price competitive with the ones of less than half the area used with formats like DX and Four Thirds. The 5D might already be achieving most of the available economies of scale, and still costs $2,000 more than the 20D, $2,700 more than entry level DSLR's.
The price gap to "most affordable 24x36mm" has only shrunk from $3,000 three years ago when Kodak and Canon released ther 24x36mm DSLRs: then it was $5,000 for the cheapest 24x36mm, the 14/n, compared to $2,000 for smaller format DSLR's like the Nikon D100 and Canon D60.
On point (, it is with the shorter focal length lenses specifically for the 1.6x format where Canon lacks "fast top quality lenses".
In particular, for many photographers, the wide to moderate telephoto zoom is the most heavily used lens. Canon's best offering is the 17-85 f/4-5.6 with slow, entry-level apertures, leading for one thing to a distinctly dim viewfinder image in low light. For comparison, a lower price gets the Nikon 18-70 f/3.5-4.5 (or the Olympus 14-54 f/2.8-3.5), and at the top of the line, there is the Nikon 17-55 f/2.8 (and the forthcoming Olympus 14-35 f/2).
Another more specialized Canon 1.6x lack is 180º fisheye, which Nikon DX has (and Olympus Four will have soon). Canon advertising explicitly uses the
lack of such fish-eye coverage with 1.6x as one reason for going to 24x36mm format instead. If I wanted 180º fish-eye, it would instead be a reason to prefer Nikon DX!