I suppose it's possible he could become a better passer, as much of that type of skill is "knowledge" of the game, which can be aquired over time.
Don't see it possible he'll become much better at ball-handling, though. It's very rare a players improves that type of a skill at this point in their career.
The only reason Bradley is able to competently play PG currently, from an offensive standpoint, is due to the offensive creation abilities of Pierce. Bradley is really just a combo-guard, that is so [dang] good defensively, it allows him to be a starter.