Russ, the answers to those questions are as follows....
By Milton Ave, I think you mean Vineyard Ave, which is also US44/NY55, yes, the footings are in place and a pre-fab bridge will be put over the roadway.
There is an existing bridge which 9W passes over the ROW. The center of that span is a CNE built concrete arch, and the outer lanes are pre-stressed slabs. There will be a ramp from the west side of 9W down to the trail from there.
At South Riverside at Tony Williams park, I can't answer that, I know it has come up and believe or not it is on the state DOT's wish list to restore that. The other bridge which crosses the empty ROW right now is being replaced later this year, so they are serious about extending the west end of the trail. Currently the trail is closed in the middle for the bridge project.
You can visit the Hudson Valley rail trails web site, they do talk about the Eastern extension, http://www.hudsonvalleyrailtrail.net/
And in other local rail trail news, last year the 11 miles of the Wallkill valley passed into the hands of the Wallkill Valley land trust with the intention of extending the Wallkill valley rail trail from Rosendale to Kingston.
And to stay on topic, the parking is much better, the crowds have left, that is not to say the weekend is not busy on the bridge, but the insanity has quieted down.