As I said, a few ideas.
c2c 8 carriages short is hardly a major worry, 2 units from 17. That could be made up from other 375 sub classes if really desperate.
I think I'd assumed all the 365s would go over to SE which would more than compensate for the 375/7s.
On the GN it would be a new fleet, ie all/more 387s (where their speed can be used unlike south of the thames). 321s to GA and 317s retired? But again, I thought EC IEPs would run some of the services FCC does now?
377s can of course do DV, but only some actually do. 319s already all do - main advantage would be removing 455s (which realistically cant) from the picture to have an entirely DV fleet. Granted all might be gone by AC conversion time anyway! DC to AC is something I think is a good idea, but cant see how it would be done in practice given the need to keep the system running, the impossibility of parallel and that even a handfull of changeovers are expensive and difficult. The complexity of the Southern Region defies a logic scheme for me !
Ref 170s, Scotrail could release a few as mentioned previously (presume they plan a new EMU order soon?). post ex Chiltern 172s, Chase and 350s LM should be able to release more 170 /5 &/6 than XC would have released 170/3s so actually XC could be strengthened - admittedly I didnt spell out that point.
If the LO 172s go to LM then their 150/153s could all be released with 17Xs on all DMU services.