No doubt there are significant costs and equipment utilization factors where an electric-diesel engine change is made. MILW made much of this when they abandoned their electrification, but the reality was that the diesels ran straight through from Chicago to Tacoma and the Little Joe electrics were added as helpers for the 3 mountain districts between Harlowton MT and Avery ID. If coast division substations could have supported the Joes, perhaps they might have carried them through the gap and then run them from Othello to Tacoma.

When GN abandoned their Cascade electrification between Skykomish WA and Wenatchee WA in 1956, one of the alternatives examined was to extend it to Seattle on the west and Spokane on the east. This would have given them the option of turning all diesels back east at Spokane. Had they done this in 1956, then attractive options today might be to extend electrification east from Spokane to Havre, or perhaps west from Spokane to Pasco or even Portland! Today's BNSF train counts are approaching the point where this might be justified.

The point for the transcon; from wherever you start the electrification on the east end, run it all the way to LA. That way you only have to change engines once.

With todays AC diesels, I also wonder about the feasibility of a electric-diesel that would take AC from the catenary and step it down to the voltages needed for control and traction.

At least once during a very cold winter period in 1949, the MILW ran a train downgrade in regeneration during the evening peak power use period at the request of the Washington Water Power Co. In doing this they may have saved the grid from going down.