Except that Moffat and company planned around the "Hobbit" and "Star Trek: Into Darkness" schedules, which is why they're shooting "Sherlock Series 3" after production wraps on Doctor Who's 50th Anniversary special.
I suspect that Matt's casting in Gosling's film will mean that we're going to be in for a very long wait for series 8. They could start shooting it later this year depending on how large Matt's role is...but I don't think we'll see series 8 until well into next year, if even then. They've yet to even commission it yet right?