PDT has Dash 8-100s and 300s. Almost all of the old Henson 100s (some of the first Dash-8s produced) will be parked in the next couple of years. The old Allegheny 100s and the 300s may fly another few years. I think AA will be turbopropless by 2020.
Q400s are just too expensive. If they could build a Q300 with q400 speed at a much lower price point you might see a major airline bite, but then you have the regional airline pilot shortage to contend with.