Hi!
Please give a quick PRO or CON response as a basis for discussion.
My opinion: if it ain't broke, don't fix it. It's ok to use new syntax in new code, but spending time on changing perfectly working code just to use new array syntax looks like misplaced effort to me.
There are new features that I would have more support immediate change, like $this in closures - that makes code much more readable and less bug-prone. Even then, I'm ambivalent whether we need to touch the code that much, but I see a point of cleaning it up. But with array syntax, it's just a different syntax, and I don't see a lot of reason to mess with existing working code just to use it.