Opinion – Kojima Made The Right Choice Picking Sony
It sounds like Kojima had a number of options when it came to partners for the first project from his post-Konami iteration of Kojima Productions, but I think Sony was the right choice.
First off, you can't underestimate the power of Kojima's stated comfort level with Sony and PlayStation products. Now that he's in charge of his own independent studio, it's important to have some things that are familiar instead of a sea of uncharted waters. Through his years with Konami and the close relationship the Metal Gear franchise had with PlayStation systems, I'm sure Kojima has a good rapport with executives like Sony's president of worldwide studios Shuhei Yoshida and Andrew House through the latter's days in marketing for Sony. Hopefully this kind of pre-existing relationship with Sony cuts down on poor communication and both sides understand what's expected of each other.
Kojima Productions' debut game will appear on the PlayStation 4 first, but it's not an out-and-out exclusive. The lack of full exclusivity may bring up the question of why make it exclusive at all, and why didn't Kojima sign with a third-party publisher who could reach more gamers on more platforms simultaneously. While I don't know any of the deals Kojima had on the table nor the details of his contract with Sony, I'd imagine that the exclusivity period alone brought in some extra cash above-and-beyond what Kojima would garner on the normal open market.
This brings up the possibility of Microsoft. Sony and Microsoft may both be console manufacturers with stables of first-party dev houses, but currently Sony is simply ahead of its competitor. This is certainly the case in the install base of the PS4. While that may be just a number to gamers, it adds heft to potential sales numbers as well as puts Kojima Productions in position to possibly benefit as corollary of Sony's success.
Microsoft has done well with its timed exclusive for Rise of the Tomb Raider, but Xbox head Phil Spencer (in an interview with Gamescore this year) said that paying for outside exclusives isn't in the company's long-term strategy (it's at 5:57 of the video).
The console wars could also come into play in the fact that, at the moment, Sony has the luxury of time in that its console sales have not seemed to dip even though there's been a lack of new titles published by Sony. If Kojima's project takes more time and money, Sony's not in the spot (yet) where it has to rush it to market because it may need a cavalry. It's an extreme example, but perhaps Sony's patience with The Last Guardian shows it has an appetite for waiting when necessary.
On the tech side, so far in this console generation, developers seem to have gotten more out of the PlayStation 4. While this will likely even out as the generation continues, if Metal Gear Solid V is anything to go by, we'd rather have Kojima with all the firepower he can use.
Kojima no doubt had his pick of the litter when it came time to make a deal, and this is simply speculation on a just a handful of the variables involved, but from where I'm sitting, it looks like he made the right choice.