So, this is a huge debate in transit circles, but it really shouldn't be.I am for spending taxpayer money once.
It is a waste to rebuilt an area for express bus just to rebuild it for BRT.
It is a waste to rebuild an area for BRT just to shut it down and rebuild it for LRT.
It is the same as whether the Canada Line should have been built with provisions for 80m trains, or the entire Canada Line + Legacy Lines built with provisions for 120m trains.
But it is pretty easy to show it is wrong much of the time, if you think about the time value of money, or about how you can build more, earlier, and maximize social welfare while still saving money.
In London's case, as was true in Waterloo, the optimal investment is pretty minimal. Ion shouldn't be held as a triumph - it isn't faster than the bus that did the route before, it isn't more frequent than the bus that did the route before. It is solely a quality of life and real estate focusing play. Which is fine. We just shouldn't act like it is a hugely consequential transit thing, even though it is a hugely consequential city building thing.
Until London has a lot more money to invest it will not be able to move the ball forward on a consequential transit project. It will just be investments around the edges, like the queue jumps contemplated in their official plan.