Does this imply anything about Gronk?
I don't think so. I think it's just an attempt to fill that "move TE" role they've been missing since Hernandez, well, you know...different role than Gronkowski, who is the in line guy. Could say they're not that psyched about Amendola though.
Regarding Mankins, I think he's fine, it's just that the Patriots tend to try and move on a year too early rather than a year too late. Remember they said the same things about Seymour and he still had a couple of decent years in Oakland.