It would be good to start using them on Stansted / Cambridge services - at least to get the WA drivers used to using them on a regular basis - particularly if there are more units available than needed for the current cut-back GE timetable. Plus it would facilitate withdrawal of the clapped out WA Class 317's.
Out of interest, in a post Coronavirus world, i'm wondering how the Norwich to Stansted service will stable at Stansted once the 745/1's are in service. Currently a 755/4 can draw up to an 8-car Class 379 and share the same platform at Stansted and vice versa, but how will that work once the 745/1s are fully deployed?