I can’t see the 365s going back on DC as it’s a fair amount of work involved.
On paper, it would be feasible to replace some of the GN 387s with 365s, and send the 387s south of the river, either directly or indirectly replacing the 313s. There’s 6x 387 diagrams which do peak Peterborough work for a start, and for the remainder it could be theoretically be done by separating off the Ely services and making them 2x365, especially once Waterbeach platforms are lengthened as it removes the need for dividing at Cambridge. The remaining 387s would then be concentrated solely on the hourly Kings Lynn service.
I wouldn’t advocate the above though, as it would introduce performance risks, as well as perhaps being politically problematic.