Sony can't outperform Microsoft in terms of money. XD

Let's assume FFXV would sell 2 million on Xbox, which by itself is probably going to end up being a conservative guess. Let's also assume that the game is 59.99.

That's $120,000,000 that SE would be losing by not putting it on the Xbox One. That's $120,000,000 that SE won't have made to help make their next title.

SE already does enough by making titles like KH 2.5 remix exclusive for Sony. They don't need to hemorrhage money to stay in Sony's favor. It's bad for the company and gamers. 

Unless Sony has a spare $120,00,000 lying aroung (they don't), they would be wise to let SE do its own thing.

Shareholders of the companies you mentioned wouldn't want that. We're moving towards an ever-increasing multi-platform world these days due to the choices available to consumers.

I also don't believe that the gap between PS4 & XB1 is big enough to warrant completely dropping the latter.

I don't think Bloodborne is a good example either. Japan Studio are co-developing it, like they did with Demon's Souls. From Software are still a developer first and foremost who do jobs for publishers, such as this one. They have no overseas distribution method so a title with a large overseas audience (like a Dark Souls-esque game) would at least need an international publisher on board).

Square Enix are a publisher first and foremost, with some internal development studios. Despite the ridiculous amount of time they've spent on FF XV so far, they don't need any assistance with development. They don't need a publisher like Sony to fund them. They can do it all themselves.

Perhaps Sony could indeed partner up with Square Enix and release some kind of Final Fantasy title exclusive to PS4. But why would they want to at this stage in the game? The FF brand has been hugely damaged this past generation. They'd be better off investing in other exclusives. Or, as they seem to be doing, investing in franchises with strong futures ahead of them - see their exclusive marketing of Watch_Dogs or Destiny.

But in any case: I don't see an exclusive FF being beneficial to either Sony (in terms of how much they'd have to pay to secure it) or Square Enix (diminishing the brand even further by removing a large pool of potential players).

I don't see how it's worth it.
it's like exclusive content. waste of money.

Better invest in new IP's/studios

SE doesn't make $60 off each game sold, I remember a thread a while ago making a chart of how much of the $60 the developers actually get, it was around $7.

You are talking about the old Sony, that had a massive lead in sales and an abundance of cash to moneyhat games. PS4 isn't a big market leader and Sony as a whole is bleeding money.

You basically explained it yourself, if the games already sell massively more on PS platforms and are basically often identified with the PS brand, why should Sony bother paying publishers to make them exclusive? I'd wager that the people that buy MGS or FF on Xbox are not going to buy a PS console for any of those games, at least not alot of them, most of them just buy it because it's available on their console of choice and wouldn't if it wasn't.

So why take the games away from those people, if you won't benefit from it anyway? Just get an exclusive marketing deal for those games and you're very much set, no need to pay huge sums to ensure exclusivity.

That is far more money than they would get from 2 million in sales you are taking zero other factors into account as, for a hard copy, the store, microsoft, production, and so on all taking their cut from the $60 on the store shelf. They would simply do whatever made the most money, with the current gen the difficulty yo port over is far lower so the money offered needs to be higher and higher as both install bases grow but it is knowhere near this high.

Edit: That's right person above somewher $7 dollar, so that's $14 will a few mill taken off to port it over and a nice friend discount, a cool $10 mill seems like a safe deal to make

There's no point for Sony to buy 3rd party exclusives if the multiplats sell considerably better on the PS4. If Sony wants to get 3rd party exclusives, they'll do so through having their 1st party studios co-develop (e.g. Japan Studios & From Software) and increasing their lead over the X1 even further.

Well to be honest Sony currently has the biggest amount of 3rd party exclusives I can remember, since early PS3 years, probably because their 1st party line up is the weakest since the same time frame.
- LBP3
- Bloodborne
- The Order 1886
- Ratchet and Clan Reboot

And smaller titles in:
- Helldivers
- Hohokum
- Resogun
- Counter Spy
- RIME
- Everybody's Gone to the Rapture

Why not big 3rd party AAA exclusives? Well it's obviously money, something that Sony is in no luxury to throw around.
Plus the games mentioned are already heavily related and identified withPlayStation, as you said, they will easily sell better on PS than Xbox, and in other location where they matter - Japan, they are not on Wii U, so pretty much exclusive.