In an ideal world, Pearson would have been doing small-scale expansions consistently over the last couple of decades, instead of waiting for the current situation of severe overcrowding and a wildly inadequate terminal footprint.
I feel like this is a common Toronto problem: build something major and then do nothing, until conditions deteriorate far enough to require a comprehensive and expensive "revitalization." Rinse and repeat.
I know they built the "connector" or whatever it's called for ground-level US gates at T1, but that thing is so cheap and shonky that it doesn't count.