Issue is METROLINK electrification (partial or otherwise) not HSR. Metrolink decisions on electrification have little to do with meeting HSR requirements, fictional "Palmdale Base Tunnel" or otherwise. The only design criteria for electrification would be, like with Caltrain, that whatever is done be compatible with use, someday, by HSR trains that might use the line.

As a practical matter, I don't see (from the map and a look at Metrolink's schedules) the Lancaster (Palmdale is a station stop) Metrolink line getting electrification any time soon, at least beyond Santa Clarita (La Princessa, where most off-peak AV Line trains end).