Thats what GO is for, long haul commutes. Subways are for local service. When I keep thinking Eglinton is not even getting a subway, no DRL, etc and yet there is an extension into the 905.
Just because the Subway has suddenly been extended from Downsview to HIghway Seven does not all of a sudden make it for "long-haul commutes". Practically, yes, a lot of riders will use it for this purpose, but providing the subway in this area also provides local service for the residents of the area, and useful connections to VIVA / GO Train and GO Bus. It helps us to establish a more comprehensive network, and in the long-run, I believe that this is a good thing. The benefits of those items need to be factored into the equation.
Besides, having the subway in this area increases connectivity and the attractiveness of GO Transit for long-haul commutes, as passengers can disembark at Downsview Park GO Train Station, or catch a train from there to downtown Toronto. It's possible that riders in this area will see GO Transit as a good alternative, as their previous station (York University Station) was poorly placed and poorly connected to the transit network. This is a good step towards future integration between GO Transit and the TTC.
I can understand what you're saying regarding going North of Steeles to HWY 7, but my guess is that after York Region agreed to pay 1/3 of the capital cost, the TTC jumped at the opportunity. It's not often that someone
offers to pay for infrastructure, and if you're the TTC, you take what you can get when you can get it, I suppose. Extending to York University is good policy, regardless, IMO.