Ticket demands isn't necessarily increased with population increase. That's where argument is a slippery slope.
It isn't a question of total population or size of the fan base, it's the ratio of fan with tickets to fan without them that counts and I'd say it is comparable. Finding a hockey fan in Montreal that never saw a live game at the Bell Centre is a lot easier than you think and as I said increase in population does not necessarily equal increase in fan base.
I wouldn't use that sort of line to predict a second franchise in Montreal anytime soon or some decades from now personally. There's tons of other factors you need to consider, such as the general wealth of the market.
Fair enough, though one would have to assume that people are moving to Montreal for increased wealth opportunity, it's the most basic reason for population increase (although sometimes it's incredibly relative to the neighbouring surroundings). That being said, I didn't actually predict it would happen at some point in the coming decades, rather it's not something that is even worth exploring at this point, but it could possibly happen at some point.