The only things I think Square-Enix could realistically do for Sony now that'd result in some exclusive games for PlayStation are Vagrant Story (remake), Xenogears (remake), and Einhander (sequel). Also maybe Ergheiz, or co-developing a more story-driven JRPG campaign mode for a Gran Turismo game. Final Fantasy exclusivity is probably dead going forward (if it's PC Day 1 that's the same as not being exclusive), Dragon Quest is going to be at least PS & Nintendo Day 1 fare, the smaller games also come to Nintendo and some even to Xbox, etc.
With those prospects I don't think Square-Enix would be worth $1 billion in investments, not unless they had big transmedia plans for stuff like FF and DQ; the former in particular also seeing some creative transformations that massively expand the selling potential of mainline titles in the series. Otherwise I'd say $100-$250 million tops is a more realistic investment into S-E.
The rest of that money could be spent on 2P deals with a bunch of other devs & pubs for various AA titles and maybe a couple AAA titles between new and legacy IP, with SIE studios having smaller team to help in co-development.
