The Tottenham situation is very interesting. Due to the game of musical chairs being played around North Melbourne / e-gate it seems to me to be getting more use ATM than is has for years as rakes of flats are moved in and out of there to Dynon.There was some talk that Totty would house some kind of maintenance or stablling for Airport services. With inner city land selling for millions to developers I cant see a massive train maintenance facility being built there.
With pressure on to free up more industrial land close to the city for development much of the activity conducted at North and South Dynon will probably have to move to intermodal style terminals such as SCT is developing and the one touted for Beveridge by Qube plus Somerton in the not too distant future.
This will render Tottenham pretty much surplus to requirements however it is also being used ATM as a staging point for a lot of works trains which will have to find a new home. Much of the junk rollingstock is now gone and I reckon the rest will follow suit fairly shortly.
I am not really familiar with the layout up on top of the dirt mound but if you ran the SG lines out as far North as you could and extended both legs of the triangle via longer bridges then removed all that (almost definitely) contaminated dirt would you end up with enough room to run at least one extra pair of tracks adjacent to the Suburban pair?
Of course that still only gets you to West Footscray. From there it is either "going down thank you, going down" or property aquisitions to get you closer to Footscray proper. Once at Footscray however I cannot see a viable alternative to a tunnel or 4 as there are just too many obstacles to widening the corridor further.
No matter how you cut the pie its still messy. Come up in Totty and you still have those embankments to tackle and then you are most likely going to have underground platforms at Sunshine as MARL forms the western part of the SRL. Tunnelling all the way to Sunshine is an expensive option, possibly one that might eventuate to avoid as many issues like Totty redevelopment, the ARTC mainline, whatever those embankments are made of and some very complex track work at Sunshine.
When you look at current infrastructure spending, the works at Sunshine alone are going to run into the billions, with a fair bit of compulsory acquisition. Along with someone kind of underground arrangement for MARL/SRL you still have aboveground work for the future Melton electrification. If regionals end up going in the new tunnel is their an additional decline structure or flyover to get them in the right place. This is in addition to extensive modifications to Hampshire Road, Ballarat Road and St Albans Roads bridges. It all makes the Totty seem simple in comparison.
Not that I like throwing spanners into the works (actually I do), I agree, Sunshine will be messy, but only if you only look at land available for rail outside the context of the road network and the constraints it places on the station.
The 'messiness' could, mostly, be sorted out by pulling down the Hampshire Road bridge + two offramps on the eastern side and replaced with an underpass closer to how the original road would have crossed the railway (around the southern side of the platforms where they currently sit).
At the station itself: No more Hampshire Road overpass (and sorry to say the Signal box on the down end of the station), and removing the pedestrian ramp that takes up the space on the island platform would allow you to put in supports for another island platform elevated above the RRL concourse everyone entering the station (except for the western side on to platform 4) must enter the station going up for the concourse, so why dramatically change that by putting new platforms underground?
There'd be disruptions, but *whistles*, we've sort of got an idea about building above active railways (see CD9, Reservoir, soon to be through Preston and Coburg on the LX removal programme). Elevated platforms then give you another advantage: if Tottenham yard needs to stay intact/useful for freight (I realise that's debatable, but just say it needs to stay intact), well, keep the tracks elevated from Sunshine all the way to somewhere just before West Footscray where you can build a Bella Vista-style (Sydney Metro) tunnel to trench to elevated structure/transition. Or keep it elevated from Sunshine to the mounds just after the SG junction then send it back to earth, taking up space from 2 roads through the freight yard on the surface for a 1km or two then transition to tunnel just west of West Footscray. That shortens the tunnel considerably, yet would come with an increased cost due to the elevated section (using general rule of thumb that elevated versus on grade = elevate will be more expensive to build) but possibly avoids a lot
of pain in reconfiguring Sunshine (i.e like rebuilding things or building underground platforms) et al.
I'd possibly even position the elevated MARL platforms a little further southwards so that on the down end, there's more room/length to send a grade-separated pair of tracks back down to earth and then further down under Anderson Road in the Deer Park corridor and another pair to the airport above the existing corridor.
(This all basically locks in Geelong and Ballarat to use the MARL tracks from Sunshine to the city and the existing RRL pair which has platforms at Southern Cross-Footscray-Sunshine-Ardeer-Deer Park-Tarneit-Wyndham Vale and Deer Park-Caroline Springs-Rockbank-Cobblebank-Melton would be electrified and be used for the two new metro lines).
By retrofitting effectively everything above (except for rebuilding Hampshire Road under the at grade tracks to the south of the existing platforms) the existing infrastructure you can pretty much leave everything at grade as is: The Sunbury/MM1 tracks stay the same and the Regional Rail Link tracks, as they are now, get electrified and become the Melton/Wyndham Vale metro and Bendigo Vline pair. Still having the flat junction for Bendigo and Melton/Wyndham Vale isn't ideal but at least they wouldn't be ripping everything up to reconfigure the entire station precinct. (Also, if the MARL will be built like Rail Future Institute's ideas - i.e Bendigo via the airport - great, but I say that would be a long-off into the future second phase).