I've always assumed that his use of electric bass came down to his allegiance to Bob Cranshaw, who happened to switch to electric bass (due to back problems, I read somewhere). When I saw Sonny in Detroit last year, Cranshaw was on upright, while he was on electric the previous two times that I'd seen him.
Regarding who Sonny should play with, I think he could poach Joe Lovano's Us Five group for some gigs or recording and make some great music.
Poach the band and fry Joe?