The big issue with moving the VIA rail north of downtown is that it forces another transfer to public transit or a longer uber ride for many trips into Montreal. While I don't have access to data to back this up, I do understand that the majority of people choosing to take the train from Ottawa to Montreal instead of driving do so because it is more convenient than driving if your destination is in downtown Montreal. If HFR is going to attract more riders it will need to compete with driving to gain additional ridership from people who would have otherwise drove. This would require playing towards the strength of the train, easy access to a downtown that is accessible without a car. Addition an additional transfer to a crowded metro train or a need for a moderately long uber ride makes the entire process less appealing and makes it less likely that drivers choose to buy tickets instead of just driving to Montreal. This gets worse when you consider how many people could be going to destinations off the REM route and would therefore need to make two transfers in Montreal to get to their destination. Transit gains ridership when it is made more convenient. While adding frequencies and improving speed does improve convenience, relocating stations and splitting services risks negating these benefits.