What about maybe the Chiltern Main Line from Banbury - Stourbridge Junction? Would be great for conductor mode, and for a new lock in the form of the Class 68.
Anything Chiltern related more likely to be Marylebone centric. Oxford to Birmingham in BR days, now that would be quite good especially via Solihull, the route is moderately scenic for the South Midlands. Also any modern day iteration north of Banbury is going to be stymied by no licence for Cross Country, which immediately loses you two trains an hour in each direction.
