HSR is worth it in some places, but the planning, engineering and construction of any HSR line, at any speed, will be a major challenge.
I think the "lowest hanging fruit" would be the Toronto - Pearson - KW - London line at a max speed around 250 km/h using existing ROW (e.g. the UPX corridor in Toronto) in urban areas.
Even there, I foresee major obstacles. These include:
- sharing space with the CN mainline between Bramalea and Georgetown. In some places - like downtown Brampton - I think that the only option would be to elevate the HSR line on a concrete viaduct, which will bring downtown Brampton NIMBYs out like moths to a flame.
- expropriation and trenching of the HSR line just west of downtown Guelph.
This is how the line looks now. I imagine they'll have to dig up the entire street and build a cut and cover subway for the HSR line for a few hundred meters. It won't be cheap.
- Then there's the fact that at HSR speeds, every crossing has to be grade-separated and the line has to be electrified in its entirety.
Anyway, I'm not saying it shouldn't be done, but I don't think we'll be riding HSR trains for at least 10 years and it will generate a lot more controversy than people are willing to admit.