I'll start with the easy one - for the northern "mouth" of Winthrop Street, it would be valid to add a highway=pedestrian area on top of the existing linear feature with connecting nodes. The usual rendered output of that looks like a uniform grey like a pedestrian street but having whatever shape you gave it. You can see an example of this along the west edge of Grand Parade, with a bunch of routable linear pedestrian streets like Tuckey Street padding through. I'm going to have a look at the other examples you gave.