Well, this is quite interesting.
I'd heard of rifts between The Last Guardian's creator Fumito Ueda and Sony for a while now, but with him being in the crowd at PlayStation's Press Conference and the game coming next year, it seems those divisions have been smoothed over.
Having said that though, some of those cracks may be visible in this GameInformer interview with the director. When talking about why the game got delayed and why it didn't appear on PlayStation 3, he said:
Orginally, this game was designed for PS3. Assuming that all of the game architecture and all of the game design was suited to deliver the experience I envisioned, given those assumptions I think it would have been a good product.
And just in case that comment was misleading in any way, technical limitations probably only existed up to the PS2 generation. From PS3 and PS4, especially considering the delivery of expression, motion, etc. – from those elements, it's a matter of how the game is designed, but it's not technical limitations at that point. The PS3 was not restricting me from doing something.
On the delay specifically, he said directly:
There were multiple reasons. There are always delays in production, as you know. Technical being one of them, but there were many others that were out of my control as well.
The reason for all this tomfoolery? Sony, it appears. When asked who decided to push the game back, Ueda said:
It was pretty much a corporate decision by Sony. And that's where we'll leave it. [laughs] Sorry.
Now, this isn't proof of anything, and I don't want to draw unfair conclusions. The way I read this though is that there was some kind of disagreement on how to proceed with the game.
I may be reading into nothing too, mind.
It doesn't much matter now. Things appear to be back on track and the game is coming in 2016. I'm totally on board too. The footage for the game looked stunning.