Before long, I can see everything that can accommodate deckers being operated these. The exceptions would be those services which can't due to route clearance issues e.g. X8, 24, 126, Bath 5 etc. or those where it would be dramatic overkill to operate a decker.
I can also see the fleet being harmonised with cascaded. I can see all B7 deckers either Geminis or ALX400s going except 32001/32002/32012 and the Streetdecks too. Replaced with a standardised decker fleet or either ADL or Scania E400s and B9 Geminis.
Singles will be more of a mixed bag, the Darts will go sooner or later and where possible anything will be replaced by Streetlites. Except the specialist services which need Solos, the newer B7RLEs for capacity and the longer E200s.