I don't see a fit on the Celtics roster for Gordon at either the 3 or the 4. I like our depth at the 3 with Crowder, Brown and sometimes Jerebko. At the 4, it would push Horford to the 5 more often which is not ideal for him at this stage of his career.
Gordon got some good PR with the Dunk Contest (a fool's gold event, IMO) but I am not sure he can shoot. That doesn't work well in Brad's system.