A denial like “it’s simply not true” is frustrating because it doesn’t say what isn’t true, but Frank Marshall at least provided some other bits of info to The Hollywood Reporter when shooting down the current rumour about Matt Damon coming back to the Bourne series.
Justin Lin is working with Andrew Baldwin on an Aaron Cross script/story that they pitched us a few months ago. I talk to Justin all the time and the script is not ready. It’s a summer movie, and if we don’t start preproduction now, we can’t make next summer. Therefore, it’s a wise decision to move to 2016.
So he doesn’t explicitly say Matt Damon isn’t coming back. He really doesn’t. “It’s simply not true” would still apply if Damon were coming back but wasn’t the reason for the delay.
But I still don’t believe the rumour is true. Not on current evidence.