I was thinking 25 kV AC SCS-Sunshine-Airport-Beveridge-Wallan - (i.e. along OMR-E6 alignment, with opportunity for electrification on to Seymour).
I think the reality will be more like what PIMM has suggested. Broad Gauge 4 Eva!
Understand and concur, but extend this to Ballarat and RRL to Geelong making all outer suburban services (V/Line regional) to become AC rather than DC extensions?
Practically speaking, the extensions of the suburban network to WV and Melton will have to be 1500V DC and BG, simply because they will most likely be interacting with the existing network in some form.
It is almost certain that express tracks will be built along both of these routes through the extended suburban area. The question of whether they will be electrified at all is not a certain one. The most persuasive factor in favour of doing so would be the ability to use an express tunnel route from SCS-Sunshine. That said, if the tunnel were instead used for Airport and WV/Melton services there would be no reason to electrify the longer routes at all. Remember that 40 minutes to Geelong and 60 to Ballarat is achievable using the existing rollingstock and alignments - the only complication at present is the speed through the metropolitan area.
Returning to the subject of the thread, electrifying standard 1500V DC to Wallan and reinstating the Somerton link with additional track pair from Craigieburn - the simplest and cheapest option here - would enable frequencies up to
- 3tph peak to Seymour/Shepp via Upfield, as assumed by the Regional Network Development Plan
- 15tph peak to Wallan
- An extra 7tph peak to Craigieburn
- 6tph peak to Upfield
Giving us 24tph through the Northern Loop, 4tph direct North Melbourne-SCS-FSS using paths currently available for Sunbury services, and of course 3tph to the Country lines.
Obviously justifying 15tph to Wallan is stretchy at best and more of those could run to Craigieburn.
The point is, you can run a service with an excellent frequency to everywhere that needs it without getting frothy and building absurd and unnecessary electrified infrastructure.