So, in short, what we currently have looks like:
Were Professor Currie's proposal to be implemented, it'd look something like:
Though why not stop there? There was, a while ago, a proposal to build an underground line from North Melbourne, across the inner north (including Melbourne University), through to the Eastern Freeway and along the centre of that to Doncaster and the suburbs. Were that to be resurrected and combined with this plan, it would start to look like:
Of course, the chances of seeing anything of this sort happen are not good.