OPTION 1. Converting the line North of Dunolly and re-opening the Maryborough - Ararat line
This would mean all SG services would travel Mildura - Dunolly - Maryborough - Ararat - Geelong - Melbourne. It would include conversion of the Murrayville branch, but the Robinvale (Manangatang) and Kulwin (Sea Lake) lines would remain as BG meaning BG services would travel via Korong Vale - Dunolly - Maryborough - Ballarat - Geelong - Melbourne.
OPTION 2. Creating a new link from the end of the SG Hopetoun Line to the nearest point of the current Mildura line (near Lascelles), this would require about 26km of new track, and woud leave Donald isolated from its current service, probably forcing that loading onto road.
Option 1 is the cheapest, and quickest solution, it also has zero impact on current passenger services, something that the government would be unlikely to want to disturb in an area where that sort of action could swing a seat at the next election. It also still leaves the door open for future work to continue standardising the network.