Should I be optimistic and say better start planning for the 60th.
I wouldn't be yet. Simply because much as I don't like Moffat's work as show runner, I'd want to know who's taking over before saying I believe the show will last another ten years (5 series at the current rate).
Hopefully Chris Chibnall.
(Actually, I honestly think he'd do a good job, much though fandom likes to rag on him for "Cyberwoman".)