It has been speculated by quite a few people that one of the aims of the tunnelling would be to remove that curve. That of course leaves the question of what happens to Rushall station itself, as one would imagine that like South Yarra, the limiting factors would become the descent into the portals before they could be levelled out for a station.
I have wondered this myself. I would imagine they would want to get rid of the kink, but on the other hand an interchange at Clifton Hill seems essential to making the tunnel more accessible to more people. Rail Futures in their unofficial proposal goes even further North, starting the tunnel at Croxton.
I've also wondered about the placement of the stations between Clifton Hill and Parkville. Usually on unofficial maps this is just shown as one station, "Fitzroy" around the site of the Gasworks redevelopment on Alexandra Parade (Really in Fitzroy North).
I found it really interesting that on the leaked (then-)TfV network development plan they had two stations: Fitzroy and Carlton. If you pair that with this image from the Suburban Rail Loop document: This map seems to me to be showing the tunnel running under Johnston St, rather than Alexandra. This maintains the kink and could even start the tunnel entrance lower (maybe just after Clifton Hill or around Victoria Park).
Now, this is just pure speculation based on little published evidence, but taken together it could mean they're considering an alignment beneath Johnston St with stations in Fitzroy (possibly around Smith St?) and Carlton (Somewhere between Brunswick St and Lygon?). This would make a lot of sense to me: Collingwood and Fiztroy are densifying really quickly, and there's lots more development in the pipeline. One of the reasons for the alignment further North was to capitalise on the gasworks redevelopment by providing it with a station, but the current proposals show a development with mostly 5-8 stories, which might not justify a metro station.
Of course, a tunnel entry further south would do nothing to get rid of the Rushall kink.
Regardless, I hope they do go for two stations in the Northern leg of MM2, the inner north is becoming quite dense and new stations would cater to this, and help make it more of an extension of the city.
From what I've read and looked at, the geography around Merri Creek basically leaves with you 3 options:1. Tunnel portal South of Clifton Hill
Allows direct interchange from MM2 to the Hurstbridge line, keeps a good service for Rushall and Merri but leaves you with the Rushall curve still. Shortest tunnelling option and so likely the cheapest.2. Tunnel portal West of Rushall:
Alignment joins the existing track just South of the bridge over Merri Creek, near Park Street. You get rid of the Rushall curve but houses, parks and roads are demolished to build the tunnel portal and a real mess is made of an inner city community. Cue outrage (I honestly don't think this will happen).3. Tunnel portal at/North of Northcote:
Northcote station is at 50m elevation, Merri Creek is at 32m (from the best I can tell via topographic maps). It's just over 1km from Northcote to Merri Pde, so with a tunnel at a 2% gradient starting at Northcote, you'd basically end up going right through the creek bed. In order to go under
Merri Creek, you'd need to either start tunnelling closer to Croxton, or drop Northcote station into a trench underneath Arthurton Rd and tunnel from the lower starting point (hey, an LX removal at the same time, win!).
In order to maintain system connectivity, you could run Mernda trains via MM2 and Wollert trains via the old alignment (Merri-Rushall-Clifton Hill and on to Flinders St) by branching at the new Northcote station. Everybody wins, but I'm betting it costs a stack more money that option 1.
Options 2 and 3 allow you to build possibly 3 stations: Fitzroy North (St Georges Rd/Pigdon St area), Fitzroy and Carlton.
Option 1 probably just gets you Fitzroy and Carlton.