Since it seems this topic has been revived, I may as well add something.
I think the system should be like this:
- Central: Melbourne Bus Link
- South-east: [???]
- East: Ventura
- North: [???]
- West: [???]
I'd go for:
West: Westrans (incorporating MBL's Footscray depot routes, Ventura's Port Melb/Fishermans Bend routes, Sita, Sunbury, all of Tullamarine except route 477, Ryans, Kastoria)
North/North East: Dysons (incorporating route 477 ex Tullamarine, Hope St, Ivanhoe, Moreland, Northern, Reservoir, East-West, Broadmeadows, Panorama)
Inner East: Ventura (incorporating Driver, Eastrans)
Outer East: Invicta (incorporating all of Ventura's Knoxfield depot routes except those shared with South Oakleigh, US, Martyr's, McKenzie's)
South East: Grenda (incorporating MBL's Sandringham depot routes, Cranbourne)
Routes that travel across operator "boundaries" should be split at a logical point, though this would mostly apply to Ventura/Invicta - so split them at Knox City.