It all depends on what EA projects a PS4 version would earn. If they think it would move 3M copies on Playstation then that would be something like $75M going to EA.
That's a lot of money. Considered from an isolated perspective, that would certainly be a loss for Microsoft. However, what would Microsoft lose if they let it go multi-platform? It would cost the XO a significant degree of future market-share? If Titanfall doesn't sell super-great then EA would probably welcome the security of an exclusive deal. If it does sell super-great, it really pushes Microsoft into a corner.
Of course, we're probably not talking about straight-up cash changing hands. Microsoft would likely put a lot of the value into advertising consideration. That's important. On-screen advertising is something console manufacturers can use as leverage. A deal would likely contain a lot of provisions like that.
Another thing to note is that I think some companies regretted exclusivity deals last gen. I actually thought EA was one of them with Mass Effect, to be honest--though, now that I think about it, it did allow them to sell old games at $60 once again.
