The funding model where, if I understand correctly, the construction contractor gets paid less (maybe none?) up front but gets 0.75ca per passenger-kilometer traveled on the system, is cool and does seem like it'd help align incentives and keep costs down.

Some of the other advantages listed in this article were enormous free wins not easily replicated elsewhere though. Somebody else had already paid for the new bridge to be wider to have a transit reservation on it. The same is true for the mount royal tunnel, which was conveniently and cleverly reused for sure, but which cost a staggering amount to construct when new.

This article calls standardization a key, but this system is entirely separate from Montreal's existing subway, and therefore doesn't match any existing standard within the city. https://xkcd.com/927/

Many of the great features suggested here (platform screen doors, full automation) are only possible on a brand new system like this. Very few cities have enough leftover rights-of-way to piece together entire new networks like this for cheap, without enormous land takings or tunneling. If you do have space for a new network, then inventing a new standard and using it makes sense; but if you don't, the best you can do is incremental evolution of the one you have.