This is one of the things I hope the city remains inefficient: Keep arguing over the Scarborough subway, until it's cancelled again and a better solution comes up.
Look at how Eglinton LRT + Hurontario LRT + UP Express, combined, costs far less than three Scarborough subway stations. Wake up, Scarborough! And European style LRTs run twice as fast as TTC streetcars. Sometimes three times as fast, especially with full grade separation like the Scarborough LRT was! No bus transfer needed for a lot of Scarborough residents that will no longer have an RT or LRT station within walking distance.
We don't want Vaughan(late/overruns), Sheppard(stubway) or Eglinton(1990s cancellation/tunnel fill-in) happen to Scarborough. Precedent has, so far, been terrible for recent TTC projects. It is so expensive that a future government may cancel the project mid-construction -- just like Eglinton subway construction cancelled in the 1990s and tunnel filled in -- especially if a financial crisis occurs (e.g. US debt default, unexpected Canada housing crash, major war/terrorism incident, etc) and Scarborough starts riding ECLRT (while Scarborough subway started construction) and realizes how great it is and what a stupid mistake they made, and whole GTA votes for a government that cancel & converts remaining Scarborough subway money into 3 brand new LRTs that perform as wonderfully as ECLRT or Ottawa Confederation. In current forecasts, the whole GO RER network and three LRTs will be done before Scarborough finishes. Scarborough will get jealous and have second thoughts, if construction is not too far along yet. Like a billon or two wasted, four billon reallocated to multiple great LRTs, and two billon to reduce property taxes again. Even a few percent of Scarborough residents would even vote for cancellation after seeing All the superior Metrolinx stuff appear so rapidly in the next ten years. That makes the truly maddening gas plant scandal look minor in comparison. How would you like to take that stupendous subway risk, Scarborough?
But if we have no choice. If the subway gets constructed, I hope Andy Byford and Tory makes sure construction starts sooner, that it goes ahead of schedule and under budget. Snoozing will mean losing.