There exists another option that should be considered at least. The current price tag for Sheppard E LRT is 800 m. What if those funds are used to extend the subway further east, instead of building the LRT line? For that amount, the subway would probably get to Sheppard and Warden.
Technically, such subway extension would cover a much shorter stretch than the LRT line, for the same cost. Nevertheless, the subway might be beneficial for a greater number of passengers, including those who do not live near it. People living further east near Sheppard, would get faster E-W trips since their bus would connect to subway sooner. The Finch E and Ellesmere bus routes could be reconfigured so that branches serving the eastern sections operate off the Sheppard subway terminus. Some passengers from Markham would be interested in using the subway, too.
In contrast, the LRT line as planned will be somewhat helpful for people living or working near Sheppard, but won't attract transfer passengers.
With the subway extension, the system would remain open for further upgrades (likely beyond the 25-year plan): both the subway further east and west, and LRT east of Agincourt.