Well, the ROW is there now. I've lost track (and can't be bothered to look) whether the H?R proposal calls for a single track with passing tracks or double track. I also vaguely recall some talk about greenfielding an alternate route near Toronto to avoid the Agincourt yard but have no idea when that stands, if anywhere. As mentioned above, adding local stops to an inter-city service is a differently thing than adding GO-level commuter service. when you start mixing service, you increase the need for more tracks, and the ROW can probably only handle so much. All bets would be off the table if HFR actually becomes HSR.
They own it and could have done whatever they wanted to do whenever they wanted to do it. I'm not privy to ML long range plans but, going by what I have heard on here, there are none.
I have not heard said rumour.