...how many 10,000s of customers we might be losing...
Somehow I find that hard to believe.
Since 10,000 is plural, we'll use 20,000 for the short end. Throw in a little inflation, we'll call a 5d3 $3000. Most people buying one are likely to be buying at least 2 decent lenses for it, let's say at a mean of $1500 each. So
Canon is going to forgo $120 million in sales (exluding accessories AND all the future revenue associated with brand loyalty) to "see what happens". I'm not buying it.
I'm not saying the 5d3 specifically will be high MP, I'm just saying there's no way Canon can stay out of the high MP market (unless they convince Sony and Nikon to as well and thereby not lose the "10,000s of customers")