I am sure that this route is in demand and his turn has come. Ideally, it will be extended to Duisburg and Wuppertal. I believe that in the future we can expect expansion to Hagen and Bochum.
Köln-Duisburg* sounds better than you have the possibility to drive a RE 1 from Aachen to Bochum or possibly in the future a Thalys or a morning ICE 2 to Berlin from Aachen. And of course the S1 from Düsseldorf Oberbilk to Bochum Hbf