On a few lenses we saw a price drop right before the release, which was Canon clearing its supply chain. But that hasn't always been the case and it has often went as Neuro described. For many of the more expensive lenses the used market stayed stable and in some cases used prices went up. Lens I have been watching because I intend to sell mine are the 300mm F/2.8 and the 500mm F/4, both of which are selling used now at the same price they were selling for new when they were discontinued.

Your best bet on a 100-400mm is to buy when they are offering the rebates. No new 100-400mm has even been announced. That being the case it could be years before you see one. There is no delivery date for the new 200-400mm, and even if there were you couldn't really conceder it a replacement since it will be 5 times the price of the 100-400mm.

So my thought is, no you will not be seeing a price drop.