15 car voyagers won't fit in Paddington with the exception of perhaps platform 1. Also Virgin Drivers don't route-learn that segment. It still would have involved at least 1 change to get to B-Ham.
Heck and I don't even think voyagers are cleared Reading-Paddington.
Of course, if the electric-spine ever gets brought back to life and Acton Wells Junction area is electrified, you could in theory run train electric train services into Euston via Oxford, Reading, Acton and Wilsden. I imagine it would add about the same amount of time FGW diverts used to take when they were occasionally routed into Marylebone.