I think MMC's would work well on the 9. Then again it doesn't really need deckers as that route gets an extremely frequent 38 service.
The 9s are already busier than the 38s from Glasgow to Cardonald/Penilee anyway. It's definitely somewhere where new buses could take a big chunk out of the 38's customer base especially since both First and Mcgills have been super reluctant to give new buses to that corridor