Titanfall will NOT sell 5 million simply because there won't be enough Xbox's in the wild. I doubt, at $500.00, there will even BE 5 million consoles sold in the US by the time it comes out. Even if there was, it wouldn't be much more than that and then you're looking at a 95% attach rate which is ridiculous.
Overall, I think Titanfall will be a hit and sell well but it's not going to have too big of an impact on Sony. Halo didn't even dent PS2 sales and Halo was 10 times the juggernaut.







