Actually, it would be good to consider such option, and estimate the additional cost.
Then, choose whether to proceed with it dependent on the magnitude of that additional cost. If the markup is 15% or 20% for 100% more capacity, that sounds like a good deal. If the markup is 40% or 50%, then maybe not, given that the need of more capacity in future is not guaranteed.
It seems that the situation with Eglinton is similar to the former case (15% or 20% markup for 100% more capacity).
That explains my reasoning perfectly. Thank you for that. The difference in cost between doing HRT and LRT (or lack theirof) makes HRT the better bang for the buck.