I emailed VicRoads (at the time) some time ago about this as I was trying to do a research project/presentation on the history of Melbourne's route numbers, and the change to the alphanumeric system. They basically said they had no plans, timeline, or further details to give. This was in 2022 though, so that might have changed!
[April 21, 2022 at 12:53 PM]
Thank you for your email regarding route numbering.
Details regarding the route numbering system can be found in the VicRoads Supplement to AS 1742.15. This document provides details regarding how route numbering is administered and managed in Victoria.
In regard to changes to route numbering in metropolitan Melbourne, the extension of the alphanumeric route numbering system is still in development and as such details regarding route numbers and allocations to certain roads is still being investigated. It should be noted that the design of the alphanumeric route numbering system will be to Australian Standards AS 1742.15 specifications.
A timeframe for when this work will be completed has not yet been determined at this stage, and given this, further details about the potential numbering system is not yet available.
Noting the above, there is no current program for the mass rollout of alphanumeric route numbers in the Melbourne metropolitan area. However, DoT continues to explore opportunities to refine existing route numbers along roads that are subject to a major upgrade as part of Victoria's Big Build.
Regards,
Department of Transport - Traffic Engineering Group