Future spin-off instead of a movie.
Bring the characters back as older people with Ava and Boyd's son now a lawman working as a Marshal under Rachel or Tim while chasing a fugitive/ criminal that is the daughter of Raylan and Winona. Loretta could grow up into a Mags Bennett type herself and be the "big bad guy."
Mad Men almost had a Sally spin off, so why can't Justified's young characters inhabit the older ones' world a few years down the line?