Who will be the Premier beyond 2015? If Wynne, I'd bet we'd see something close to hourly service on Georgetown in 2015 or within a year or two. Based on recent past practice, a Conservative government would give very little, and the NDP severely cut GO service last time they came to power.
Because the promise to do this, is much, much older? Because construction to enable this started back in 2003, and was finished in 2010, unlike Kitchener (not finished), Milton (need to sort out with CP, and spend $billions), Stouffville & Richmond Hill (I believe the second track is still in planning stages) ... and even Barrie is constrained by the construction between Strachan and Weston for some time to come (I'm not sure how far the second track goes). With nearly a decade head-start in putting in the infrastructure for the Lakeshore service increase - and 10 years of detailed promises (and another 30 of broken promises), why would it surprise anyone that Lakeshore goes first.
This is still good news for everyone though. It shows that there is a commitment to actually do this kind of stuff from the new government! They should start making some detailed promises about service increases for the next 3-4 years, instead of this vague hand-waving stuff, and then magically announcing huge service increases that weren't even in the current GO 1-year plan.