The content in the game is mostly instanced because it is a theme park style MMO by design. By having most things in the theme park style, players can decide what "rides" they go on that day. It's about ease of accessibility and less to do with limitations of any kind. Whilst it is likely that Yoshida would have preferred to have foregone the PS3 and just focused on PC and PS4, the PS3 is not really influencing any limits in the current game and it's design. Yes, the PS3 can't display as many models (for example) but the PS3 limits itself more than it limits anything the game is offering.
It's obvious, though, that any crazy things that SE wants to do (like Yoshida's example of flying around a dragon and sliding down its tail etc, I forget the real scenario painted), they'd have to stop supporting the PS3 and that is on the table eventually.
