If we did new builds and turntables here, ideally you would need a decent go most places 4-6-0 or Woolworth, that can be trusted not to hold up services for the normals on the modern network and haul plenty bums on seats.
A new build MGWR loco or one of those crimson WLWR yokes slathered in copper and brass would be a fine sight, but without any kind of a decent distance go-somewhere-to-somewhere-else private preserved line, theres not much call for things like that.