The current population levels in and around Melton don't justify electrification for at least another 20 years. alot of the land surrounding the line is just empty paddocks at the moment. I think duplication should come first to Melton then onto Ballarat.
One problem that will be created by this is it will create a bottleneck between Sunshine and Deer Park, where V/Line trains which have their own track from Southern Cross to Sunshine will have to share tracks with metropolitan trains once again, which defeats the purpose of separating them in the first place. The only solution to this is acquistion of property to create extra capacity. After all the government probably still owns the land next to the railway line anyway. But who wants to give up their house for a railway line anyway? nobody
While I do think you are wrong, and that Melton could easily justify electrification now, I think 20 years is probably about how far away it realistically is. After Melbourne Metro is built, electrification to Melton, and/ or a line to Melbourne Airport are likely to be the next major rail project undertaken by the government.
As far as Melton goes, it would include a new station at Caroline Springs, located at Christies Road, near the junction to the Boral Siding. It would also include brand new dual track from Sunshine (current Sunbury line platforms) to Caroline Springs, and duplicated track as far as Melton.
Rockbank station would also be in for a major upgrade, as major new developments are beginning in the area, and the station will begin to get a lot more use, and there is also land set aside for a possible additional station near Ferris Rd, east of Melton, an area also set for big developments in the coming decades.
Along with all of this, new stabling sidings would need to be built at Melton, something there is already ample room for.