When the wires come up and allows the Manchester - Scotland services to become elctric then that will free some diagrams, but that should see the Airport - Windermere services returning, Manchester - Scotland uses err, 10 diagrams working it out on the back of a fag packet, windermere works out at 6. The real boost for TPE's fleet will be when BPN - MIA moves over to electric operation in 2019. The problem is that before then they'll be very overcrowded on TPE north. All I can think of is to get some 180s with TPE for the MIA - BPN route, and displace some of them 185s over to TPE North.
The only isolated fleet I can see in TPE's network is the TPE South network, and possibly Manchester - Hull. Either some more desiros or class 172s for that route. A full replacment of all diesel stock on the TPE south route would free up 8 units, Manchester - Hull another 7, and it wouldn't mean excess stock in the TPE fleet later, as the 172s could be deployed on any TPE route, but they will proberbly have a long future on TPE South, and if more are needed they could be intertwined with or replacing 185s on some of the NW Routes. 4 carrage 172s by the way, may have a better home on TPE NW or TPE N, but that would depend on the diagraming requirements.