Echuca is operated by vlocities. Has been for years.
There are several issues with the longer railway lines that have seen Loco hauled car sets remain in use. Current policy has Sprinters and Vlocitys restricted to 80km/h over any lines with unprotected level crossings (no boom gates). The further from Melbourne you get, the more of these crossings there are. This restriction is due to their lighter weight providing less crash protection in the event of a high speed collision with a heavy vehicle.
This dates back a few years after a collision between a Vlocity and a truck carrying a large block of granite on the Ararat line at Trawalla. Several passengers in the Vlocity died that day. Findings of the coronial inquest included that had they been in a loco hauled train, they likely would have survived due to the superior protection provided by having the 115 tonne locomotive leading the train. It also found that if the crossing had of had boom gates, it is unlikely the truck would have been on the crossing when the train came through.
All level crossings between Ballarat and Ararat, as well as between Ballarat and Maryborough now have protected level crossings.
A project has been underway on the Echuca line for the last few years to upgrade all of their crossings, when completed (some would argue it already is) the line speed for railcars on that line is supposed to increase.
So for Vlocities to be introduced on other long haul journeys like Warrnambool, all crossings need to be upgraded. The Government have already announced that Warrnambool and Albury are next in line for this upgrade. Work has not yet started.
When work is complete on the Warrnambool and Albury lines upgrade, it is expected a modified variant of the Vlocity will be built for long haul trips, this is likely to be either a 4 or 5 car set, with similar amenities as the N sets have.