I would like to see some new diesels for in Train Sim, one of those being the BR Class 17, I find them to be interesting both in shape and history. I would also like to see the BR Class 28 (Metro Vicks), for the same reason as the 17's. I feel like both of these would be welcomed additions to any railfans collection.
As discussed elsewhere there was a Clayton available from Iron Horse so presumably Dovetail has it and may rerelease it at some point as it did with the Class 20.