I would say there is more chance of demand for a Bristol Temple Meads > London Paddington service via Westbury. I believe I may have raised this point before.
That would be interesting. But can't really see
FGW▸ ever introducing brand new services such as this though.
A year or so back though I did notice whilst looking on the Bristol Temple Meads arrivals/departures page on the FGW website, that on one Saturday afternoon there was actually such a service running on that day. From London Paddington-Bristol Temple Meads via and stopping at Reading, Theale, Thatcham, Newbury, Hungerford, etc. With a journey time of 2 hour 40 minutes.