Wishful thinking on your part on two ends. First off, both consoles will have to fight to prove themselves necessary and worthy over the base models, and they will not convince casuals to drop money as easily as a generation that just launched 3 years ago. You won't see the kind of 1 million+ launch month of the current gen, necessarily, although it is possible, that the thirst may be there for new product. Core consumers are also not all ready to jump ship, and are going to need more incentive. There isn't that built in necessity to move on from extremely outdated hardware of last gen, especially with games like Uncharted just hitting now. Furthermore, those core consumers will be the most informed about the differences between Scorpio and Neo, if things do indeed pan out as they seem now...... so the idea that the 1 years headstart will be devastating to Scorpio has to counter against other market conditions, ie the informed consumer choosing to wait for Scorpio and the other side of consumers that wants a real upgrade and chooses to wait and see what Neo has to offer in terms of tangible experiences instead of just blindly plopping down money.
Second, you make the bad assumption that MS would release another console for more than $400. They know this was a huge reason for the early move towards PS4; Scorpio, if anything, is the chance to reset Xbox as a brand; they won't repeat mistakes of the past.