This is what we propose for the East part of Toronto, specifically Scarborough:

1. Replace the Scarborough RT with a subway (Kennedy Station to Sheppard & McCowan)
2. Build a Scarborough Express rail line    (Steeles to Union Station)
3. Extend the Sheppard LRT  line to:  (A) Meadowvale  (B) Malvern Town Centre  (C) Toronto Zoo
4. Build a Scarborough Malvern LRT line (Kennedy Station to Sheppard & Morningside)
5. Build an Ellesmere BRT line (Scarborough Centre to East boundary)
6. Build a Kingston BRT line (Victoria Park station to Eglinton & Kingston)

Of particular note, and the top priority, is Number 1: Extending the Bloor-Danforth Line to replace the Scarborough RT (SRT).

There is considerable justification for this.  The top two are 1) The SRT’s ridership warrants it; 2) Service continuity for Scarborough is paramount.

Below are the reasons, and the opportunity costs.

More on the history of the SRT and the Scarborough Subway proposal can be found here.