I'd go back to San Antonio and trade 2 second round picks for Richardson.
Probably not going to happen.
Boston has made a priority out of ball movement, such that the rotation features not one, not two, but three good-sized ballhandlers to create shots off the dribble and connect the ball on the court. It's been a hugely successful experiment; all that ball movement has led to a ton of wide-open shots, and a whole lot of space for Jayson Tatum to operate in.
JT's free throw rate is a stratospheric .397, almost a hundred points higher than last year.
Richardson (much like Aaron Nesmith, and not incidentally), while he's a good shooter, doesn't do that - doesn't create for others off the dribble, is not unselfish but not a connector either.
This is a Cam Reddish thread, but it's more interesting to talk about why Jason Richardson is not such a good fit.