For most of the summer, I was against Sully starting for much of the same reason that many said here: I thought he'd be an asset on the bench being able to score in the post and could take advantage of weaker backups. Bass isn't posting up anyone; so it doesn't really matter if he's matched up against starters or bench players.
I still think that may indeed be the case. However, I do think there's another side to it.
I think there's an argument to be made that the starting lineup needs scoring punch more than the bench. At this point in their careers, Terry and Green may be better at getting a shot off on their own than Pierce and KG (collectively).
Furthermore, if Rondo is going to play slower while KG and PP are out there, it might be Sullinger's best interest to play with the starters to get post opportunities.
Then Doc can bring in Bass (who is a great finisher) to run alongside the likes of Green, Terry, and either Lee or Bradley with a second unit.
I think there's pros and cons to each side, so I wouldn't lose much sleep over it.