There's probably going to be big changes coming up in all MCs over the next 5 years. The new machines if introduced will virtually eliminate any manual flat and letter sorting as if every MC gets a CPS machine then anything rejected by a CLLS or XMS machine could be offered up to the CPS machine and if that rejects the item then it could be sorted as a manual packet.
Most "sit down" jobs in MCs will probably disappear with the introduction of the new machinery. I believe that RM want to eventually have all letters and flats sequenced together to eliminate a load of indoor work in DOs. I think it's possible that MCs could eventually sort small packets down to walk level