Currently with GWE being a TSW route, in real life, the route is a lot more busy, especially London Paddington. I think that an upgraded version would be better. A lot of people have requested for a modern. Version. And that is one of my suggestions in mind. The new route would include an increase use of high speeds passing Hayes and Harlington. And also remove platform 13 which is non existent.
The route is set when platform 13 was in existence. It's already been explained by Dtg multiple times that the route/timetable can't be upgraded due to it's age and it's methods of development being different to newer routes. Your best bet would be to request a brand new Gwe instead of an upgrade.
they have upgraded the route before despite its age, at the end of tsw2 they added PIS to stations and on trains. as well as more trains/wagons standing in sidings, with different types of freight services also added.
I meant in regards to the kind of upgrade that the OP is requesting which as Dtg have explained would require a rebuild which likely isn't possible.