1) I doubt that Jane is the boundary after which the usage can drop dramatically. In fact, Mt Dennis is a mostly low-rise area today (perhaps will add density once the LRT opens), and the Jane & Eglinton intersection is located in the flats and surrounded by parks and golf courses; it doesn't have any density and never will. In contrast, you can find some highrises in the Eglinton / Kipling, Eglinton / Lloyd Manor, and Eglinton / Royal York areas.
Most likely, the ridership does not drop dramatically at Jane, but rather goes down slowly.
This isn't something we have to guess about.
Eastbound at peak hour, ridership at jane is 2,900 pphpd. This section between Mt. Dennis and Jane, less than 1 km, is the only section of the line that is solidly in LRT technology.
Moving west to Scarlett Rd, 2 km from Mt. Dennis, ridership drops to 2,100, which is the approaching the lowest I personally would support building an LRT, and is the lowest the TTC recommends.
So in a 2 km stretch, this LRT loses nearly 1/3 of it's ridership.
Continuing on to Royal York, 3 km from Mt. Dennis, ridership drops to 1,700 pphpd, well below acceptable demand for an LRT. It's lost 41% of it's ridership in a 3 km stretch, only 23% of the proposed extension length.
Moving on to Widdecombe, 6 km from Mt. Dennis and well below half the distance of the proposed extension, ridership plummets to 900 pphpd, which isn't anywhere near LRT territory.
Now I know someone will probably mention that transit lines always lose ridership the further you are from peak point; we can't expect everywhere to be above the threshold. That's true, but that makes ECLRT unique is how rapidly the ridership drops. Of the proposed 13 km extension, only 2 km (14%) of the line is in an acceptable range for LRT ridership (about 2,000 pphpd). This isn't like other lines that might have a significant part of the line is within acceptable demand ranges.
Typically I'd support extending the LRT to Jane or Scarlett, but the issue with that is that it would add an additional transfer for commuters going to RER at Mt Dennis. It's better to terminate at Mt. Dennis and have the busses go straight to that station, eliminating a transfer.
2) Re-routing the Kipling, Islington etc buses to Mt Dennis will complicate the route structure. You still need some buses to provide service south of Eglinton.
Of course. I figure a third to a half of those busses might terminate at Mt. Dennis