I noticed your imagined workflow seemed folder-oriented, and thought of Hazel: http://www.noodlesoft.com/hazel.php

It doesn't provide the timeline you were looking for, and I don't think it can do Internet-y stuff, but it could take care of the "if something lands in _____ folder, do ____" bit if you had it run a custom script for each action.

Perhaps you could hack together your own activity stream with some elbow grease?