I never bought the economy of scale argument back when Miller made it, ehlow. It meant the uptown dog was wagged by the downtown tail, which was an RFP so restrictive that virtually every other tram maker in the world (apart from Trampower, haha) said "no thanks". If the downtown RFP had been for a 70% low floor car we could be a lot further along than we are given the delay the first time round with the derailment simulation failure.
Compared to even European light rail systems, 204 cars is a huge order, and that could be 264 if Byford gets his way. Even then, some aspects of the cars are not interchangeable. Finally, as Metrolinx will own the uptown cars there will be limits to how much parts pooling could and would happen.
The upside to Alstom would be a mature platform - more than 1500 delivered - which is already being Canadianised for Ottawa who gets worse weather than we do. There would likely be a lower CanContent because that wasn't insisted on to the same extent in Ottawa's RFP which was for a complete build rather than separating out vehicles, but 100+ cars would be a good incentive to improve on what is being done for the 34 Ottawa cars. But politically I can't see it happening. Bombardier's federal and provincial bodyguards would freak out since the company is already bleeding profusely due to C Series.