The suggestion, of course, being that we're getting a much needed update on the RPG during the broadcast. It's already got some people convinced that it's happening, but as per usual, we're here to potentially p*ss on the parade.
The bottom line is this: a PS Store page update doesn't mean anything, and it never has. We've seen this exact same scenario happen before, when multiple pages were refreshed ahead of a State of Play broadcast last year (Final Fantasy XVI included, funnily enough!). Nothing came of it.
The store page updating might not be indicative of anything, but that doesn't mean Final Fantasy XVI is forbidden from today's State of Play. Square Enix has said that the game is ready to be shown — a full trailer is apparently primed. The timing would certainly add up if it does appear tonight, especially since Sony has promised third party content.
But again, don't take this PS Store adjustment as confirmation — it just doesn't work like that. As always, we'd recommend tempering your expectations (and then if it does actually happen, you can act surprised).