How about the ECML from 1985 era. In where the class 312 and 313 in BR colours. Class 31/37/40//47 and the odd deltic....oh and the HST, and the odd metro camel from Kings X to Peterbro. The line was electrified from Kings X and Moorgate to Royston, then ran diesel to Cambridge. The electricification only went as far as north of Hitchin. But it would be an very interesting route. And DTG if you did do this route, Welham Green station did not exist in 1985 Just a thought.
The LNER 91s and HSTs will be in offlease storage at somepoint this coming year. A great opportunity to get some valuable reserarch. I think the 125 group are getting a pair of power cars also. Plus they have a working Valenta engine in the prototype.
In reality what we have so far in the way of traction for the route, it makes sense, with the exception of the 313/312 and the deltic, basically everything else has been released. A BR paint job on the 125 and its basically there. All they gotta do is build the route...easy peasy
New engine on the 125. New Headlamp clusters. New MK3 interiors. I think the cab interior is more up to date on GWR Hsts too. Might be easier to start pretty much from scratch. I think the easy, not necessarily to be a free of charge option, would be to give us a remodelled version of locos that are in tsw, to suit historical and modern routes.
