I don't know if anything on Lawrence beyond a Rapid Bus (so, Viva/Zum-style "BRT") is defensible, especially after Eglinton goes in, and if we ever get around to building a proper LRT on Kingston Road.
Lawrence manages to crawl through low density suburbia throughout most of its length and is far away from most major trip generators (hospitals, schools, major malls).
Beyond what we have, what is under construction and the identified priorities that nfitz mentioned I think the only remaining corridors in the city that warrant any rapid transit of any form whatsoever probably narrow down to:
Finch east
Sheppard from Yonge to Downsview
Eglinton East-Kennedy-UTS-Malvern (maybe)
Queensway (not much existing ridership, but a lot of development potential)
Maybe rebuilding the section of the 501 from Sunnyside to Long Branch to Transit City standards/gauge.
Beyond that, everything else strikes me as being somewhat superfluous and a "nice to have", but not really necessary.