Between Danforth and York Mills, there is Eglinton as a through route to Yonge from the East. These huge gaps, side-by-side. In these gaps: Thorncliffe Park, Flemingdon Park, and Don Mills. You can see the problem. Beyond that, there is Scarborough, disconnected from the rest of city, even before we consider a Sheppard LRT that won't go past Don Mills, or an RT that only goes to Kennedy.
South Mississauga is a similar situation, but it's only the wealthy neighbourhoods with high mobility cut off from the north. And most importantly they are not cut off from Toronto.
So I think Toronto needs to fix a disconnected road system that is isolating the east of the City, or at least compensate for it: e.g. underground Lawrence East LRT between Bayview and Leslie, DRL along Don Mills to Don Mills station, subway extensions of Sheppard and Danforth lines, and so on.