Until the team gets rid of Bradley and ET, Thomas will probably continue to come off the bench.
I think the best four guys on the team right now are IT, Smart, Lee, and Amir, though, so ideally I'd want to see all four in the starting lineup, probably with Crowder, or possibly Jerebko, at the 3.
Long term, I see Smart as a 2, so whether it's Thomas or Rozier or somebody else, the Celts will need to find somebody to play next to Smart in the backcourt. Neither Bradley nor Turner is that guy, in my opinion.