The thing to note is that not all 2.5 million people in the region actually travel frequently.
In 2011, there were 2.4 million people in Translink's area, and 1.25 million jobs. So really, only a bit more than half the people in the region commute. 6.1 million trips are made every day, and 14% of those are on transit. Of the 6.1 million daily trips, 1/3 are for work or post secondary, and 23% for personal business.
Even if it is a good value, I don't think you could entice 50% of the people in the region to buy. 50% of the people in the region don't travel that much as it is.
On top of that, you also have areas of the region that don't have reliable transit service. So trying to entice those people to buy an annual pass that gives them unlimited access to their bus that comes by every half hour only during peak periods is going to be impossible. It's one thing to get commuters to give you money, because you can target just a few hours a day with increased service. But to get more than just 1/3 of people travelling to pay for transit, you need to offer them better service all day so they can make their appointments or shop conveniently.
The problem too is if you did get more people to buy transit passes, you would need to supply more transit, as capacity in many places is maxed out. So you would need to recalculate how much you need based on how much more transit you need to supply if your plan is successful.