It sounds like a new movie won't be here in 2018 after all. Tom was asked about it two weeks ago in this Parade article...
What’s the status of another Jesse Stone?
I haven’t been able to switch gears and write it. Blue Bloods is pretty consuming. I’m not in Jesse Stone for the payday; I want to do a Jesse Stone that’s up to the rest of the book series [by Robert B. Parker], because he’s a character I love.
I'm sure I'm not the only one, but, I just see Jesse Stone as a continuation of Magnum after he got out of the navy. It's more of the sadder side of Magnum we knew was there but only came out occasionally.