I'm curious, too.
I guess there is some of the trail between the SS and Mckeesport that is finished, but I don't know what parts, how to access them, nor if they are long enough to be useful.
When I last went over the McKeeport-Duquesne bridge, I could see ramps going up to the bike bridge, but I did no see any signs pointing to or trails leading to those ramps from either side of the river.
A trail from the Homestead Grays Bridge to McKeesport would be useful even if it isn't as good as all the way to the SS trail.
Last I checked, the SS trail still ends 100 yds before the Glenwood bridge.
Mick