The S15 add on for TS is great however it really has something missing. There is currently nowhere near enough pre-grouping liveries in TS and the Urie S15 would be a great way to introduce more.
I can't see any reason why this couldn't be done as I believe there are limited differences between Urie and Maunsell S15s. Obviously the model would require significant editing, it's not just a reskin, but it'd be nice to see.