"So if the new plant is up and running by 2018, we could see the Powderhall line freed up after that..."
That would seem to be logical.
Think it needs a 'proper' campaign to highlight the benefits/opportunities and make sure some potential councillors talk about it before the May election - and CEC gets on with some design and 'how do we pay for it' work.
Anyone in Broughton, Leith Walk, Abbeyhill, Meadowbank areas want to get things started?
Obviously this link would be of use to many more than just 'locals', but I think a campaign that could point out some benefits to people who are probably unaware would be a good start.
Bring it to the attention of CCs and existing councillors too.