How about some "plug-in hybrids" from GE ... they did talk (tongue in cheek) about it some time back.

There are 2 types of dual-power locomotives in current use in the US:

Low-voltage (600-750 VDC, 3rd rail) on Metro-North, CDOT, and Long Island - the olde FL9's and various other flavors, mostly about the same power on diesel or electric. Needed for low-speed access to Grand Central Terminal while running on diesel in the suburbs. Since the 3rd-rail supply is the same voltage & DC that the motors in the diesel use, the conversion is simple.

High-voltage (25KVAC, catenary) on NJT - mostly delivered just before Hurricane Sandy (some got wet). About 2/3 the hp on diesel that they have on electric. Needed for high-speed running on the NEC and lower-speed on the branch lines for a one-seat ride to Penn. Unfortunately, the electrical gear is big and heavy enough that it's not practical to have a big enough diesel to match the power available under the wire.

All of them are custom jobs - small orders with special equipment, and ridiculout prices because the engineering and special equipment costs need to be covered over 30-40 units rather than hundreds or thousands. The prototype for a dual-power for wider use is probably the NJT one, since it's unlikely that there will be many more low-voltage, DC, 3rd-rail systems installed.

As a practical matter, dual-power would be needed for any mainline electrification, because railroads just don't change locomotives on a train any more once it leaves the origin. That would allow wiring only where really needed while still allowing acceptable fleet management. Unfortunately, as noted above, having the same power under both wire & diesel is difficult - not impossible, but difficult, and that equals $$$$ for purchase and maintenance.

A better candidate for electrification might be a switching road like Sammie's where cars are interchanged - but I doubt he's interested in juice jacks and besides the air is better in Oregon (NOT - smog alerts 2 of 3 times I've been in Portland in the summer). And what about Metrolink? Why are they running diesels?