1. (less likely) The release of a new 100-400 will take some time after all because there's no immediate market pressure
2. (more likely) The new 100-400 will be much more expensive, i.e. generating more profit for Canon, and will be an "upgrade" to the existing lens rather than a replacement on the same level - more like 24-70 mk1 to mk2.
1. There is no market pressure, nobody makes a better lens in the size/price range. That's why Canon hasn't changed the 100-400mm and the 400mm f5.6.
2. New price will be similar to Nikon 80-400mm, probably something like $500 more.