Out of interest, my 1977 Melways (my goodness has it been 40 years, how time flies!) shows the proposed Eastern Freeway with a proposed railway in the central reservation branching off the rail just north of Victoria Park, then staying with the freeway till around Kenneth St, Bulleen where it heads north-easterly in a tunnel until around Fyfe Drive, Templestowe Lower, thence generally on the surface roughly paralleling King St until a terminus at Blackburn Rd.
So presumably grabbing the centre of the freeway is still possible (the wide grass median is still there on google maps) but the land east of Fyfe Drive has obviously been sold off and densely developed. They must have made heaps of money selling that narrow strip of land (not).
However, one thing I see on google maps is that there is no attempt to put in bus lanes anywhere along the section of the freeway used by these Daft buses, even where there is the grass central reservation and despite 3 to 4 lanes for general traffic. I read that there is some allowance for buses to use the unsigned breakdown lanes which is rather dangerous, but then Vicroads was always talented at designing-in accidents.
In the google aerial I could only spot two buses in the entire length of the express section and I couldn't spot those commuter carparks. Most of the traffic is driving in the right-hand lanes so I see Victorian driving habits don't seem to have changed in 40 years at least!
There seems plenty of scope for still building a railway at least until where the grass median ends and then it would have to be underground (or land resumed). In the meatime there is also plenty of scope for a busway-type operation (like the O bahn which would allow higher speeds, or like the current Brisbane busway operation restructure at lower speeds) with exclusive lanes and articulated buses. With dual battery/OHW trolleybuses now on the market there is the potential in all of these cities to run these trunk express services with trolleybuses. It's not too hard or costly, why won't they do it?