A replacement order for the remaining "classic"-bodied E400s at Stockport, Hyde Road and Sharston depots can't be far off. The oldest ones will hit the 15-year limit about this time next year, and in any case they don't seem to be doing any work that suggests the plan is to keep them in Manchester much longer - only a couple have been painted yellow, and to my knowledge none have had interior works done, not even the soon-to-be legally required live information system.
If such an order is made, it could displace some more Streetdecks - most obviously the ones currently on the 330 - to head to Wigan, or indeed just include enough new buses to replace the older ones in Wigan directly.