PV have released the master plan for the You Yangs area.
https://engage.vic.gov.au/future-investment-you-yangs-and-serendip-sanctuary
(links on the right hand side)
No new trails are listed except maybe trail access from Little River to the Youies, and an easier link between Stockyards and the other side.
They do mention the need to fix the carpark and do some work on the existing trails, but mtb upgrades seem well down the priority list (I've only skimmed the document).
They mention the potential to
"Establish a new mountain biking hub, complete with kiosk for light meals and beverages, bike repair shop, small offices/rooms for mountain bike group use, toilets, showers/end of trip amenities, bike racks, storage rooms (for event equipment), and shaded outdoor seating area."
This seems pretty far fetched to me unless there's a huge tourism boom, as who's paying to operate a kiosk and bike store that gets traffic 2 days a week?
Looking at the response profile it seems that the mtb community was quite active in providing responses to the initial community engagement, but the upgrade focus is on education and indigenous awareness.
There's an online community engagement evening on 16 Sept if you are interested. Can register at the link above