I like the idea. A three lane street (not a reverse flow lane) plus bike lanes would be great. The third lane would allow cars to get around obstructions - such as stopped couriers and armoured cars. At some intersections, the centre lane can be a left-turn lane (say at Richmond, Adelaide, Shuter, Gould, Gerrard, where left turns are generally permitted) - I bet with left turn lanes with single-lane driving will result in very little difference in car flows as compared with four lanes, with many obstructions and no turn lanes.
There's no parking anywhere on Yonge anyway, so there won't be any issues with that.
So sidewalks will be a bit wider (about a 75-100 cm on both sides), plus the bike lanes (there is no real continuous north-south bike lane west of Sherbourne)
In Oakville's downtown, the centre lane is used where couriers stop - thereby keeping the traffic lanes open.