It needs to sell 800k units above the PS4.
Let's say August is pretty positive, and they eat away 50k.
September is likely to go the PS4 way again with the Destiny bundle and MGSV. Either way, it seems like the real game
begins in October.
They then have October, November and December to sell 800k above. October should have a significant boost: It's Halo 5, it has its own bundle, the timing is great. If it can replicate and even go beyond last year's PS4 September, let's assume they eat away 300k.
Then we get to November. Best case scenario, the CoD/Battlefront stuff doesn't move the needle much, and Microsoft goes in agressively for Black Friday again. Another 400k?
Then it's down to December, where nothing really seems to suggest they could eat another 100k lead.
I have a very, very tough time imagining a scenario where this happens, even keeping Sony's strategy completely fixed.
There are just way too many moving parts at this point to predict even remotely accurately IMO. We'll know more once we can trace out their holiday strategies reasonably well.
We don't know if those will be bundled, and while it's likely, we don't know if the CoD stuff will truly make people jump ship.