It will be interesting to see how this is built out. It will likely be built as multiple projects that end up creating the green line. You cannot build any portion west of Ramsay without the downtown portion and Grand Central (Regional and Provincial Rail) being finalized.
In reading previous articles on the downtown portion, they do say, "the design is expected to be completed by 2026, leading to construction on the downtown segment beginning in 2027."
I wish they were more specific with these dates, "design... completed by 2026", that could be in 6 or 18 months. Same thing with, "construction... beginning in 2027", that could be 18 months or 30 months. They're giving themselves a lot of latitude and I assume the timeline will be the longer of the two, meaning we won't see any substantial construction downtown until late 2027, early 2028. Giving them a minimum of three years and a max of three years and 11 months to hit their "2031" deadline. So you can say, "wow 6 years to build a line that's had most of the prep work done", but really I think that 2031 date means they'll build the downtown portion in around three years that seems about right.
Just my read though.