Electrify Wokingham-Ash, Guildford-Redhill, Oxted-Uckfield and Hastings-Ashford. This means that Southern could take over the Reading-Gatwick route and get rid of their small number of DMUs, hence significant cost savings by standardising on an all-electric fleet. The DMUs could go to another operator.
Quadruple Huntingdon-Fletton Jcn and reinstate the down slow Peterborough-Helpston. This simplifies operations, reduces the possibility of a slow train holding up an express and allows for possible station reopenings at Holme or Yaxley to serve any housing developments south of Peterborough.
Electrify Ely-Peterborough and Neville Hill-Colton Jcn. Not only good for diversionary routes, you could have a Leeds-York electric service operated by 333s, and it would contribute towards an all-electric TPX North.
Reopen Soham.
Consider electrifying to Hull, HT could use 90s for a short time until they get new electric units.