There are more choices than LRT and LIM ICTS train. If they choose to use a smaller rotary motor train, there wouldn't a need to modify the station and rebuild the entire elevated guideway, and there are many manufactures making those. Even if they choose to run more frequent 2-car LRT train, there wouldn't be the need to extend platform. However, they choose to run 3-car trains so the train can be interlined with Eglinton line, but now apparently that's no longer the case...
As for train order, yes, that's a valid concern. But how much a premium there is for a small order? 1 or maybe 2 millions per car? How much does the conversion cost? More than a billion? So this mean at least 400 cars has be ordered in order to break even. Assume SRT would need 40 cars for each generation and each train last for 30 years, the total train order won't reach 400 cars until at least the year 2315. By that time, the guideway would need to be rebuilt several time already...