So they are just "reserving" the platform space, here in Bangkok and in Luala Lumpur they actually just built the full platform - but they are running 4 cars (2 in Kuala Lumpur originally, 4 now mostly) with arrows on the platform where the train doors will be when the train stops for boarding. All they have to do when implementing longer trains. I cannot see the price for reserving the space vs. just building the platform being too much different in price.
Anyone know how much different the Flexity is from the Mark II (ART)? When I was in KL, I used the Mark II as a subway (some places elevated) and was actually quite impressed... I was originally skeptical of the Eglinton underground LRT (visioning the "LRT" platform at Union), but now believe it is actually a very good option if built correctly. If building an underground LRT is much less costly than underground subway - then it is sufficient for many lines in Toronto - especially if it gives room for more lines closer (long term).