I think there is at least a possiblity the analogy to the C300 situation holds true here. It will all come down, as others have said, to the real world performance of this camera and its competitor. If the Nikon offering is close enough in performance, considering trade offs, pluses, minues etc., to the performance of the 5dMkIII, there is a big enough price difference to be a problem for Canon. We could see the price come down. If it sells, we're stuck.
Personally, I suspect that the situation with the 70-200 F2.8 IS II, which dropped about 10% from launch prices (2500ish to 2300ish, IIRC), will also apply to the 24-70 II, and (i hope) the 5dMkII. The prices are high, and given consumer confidence levels even higher. Maybe it will be in the form of rebates (like the deals to get the 70-200 down to around $2k for a short time), maybe a permanent drop. But I'm looking for something to happen. These wouldn't be the first tech products introduced with 'optimistic' pricing on the part of the manufacturer.
My original 5d still works, and I was ready to pull the trigger on the new one at $3k. $3500 is too much for me right now. I may wait it out and save up, I may choose to get the MkII on the used market and use it until the MKIV drives MKIII prices down, or may not buy anything. Luckily my old cameras still take great photos. But one thing is for sure: I will NOT switch to Nikon.