Chippenham Platform 0:
Reinstatement of the existing south-side platform as a west (Bristol) facing bay platform with a new turnout at the west (down) end of the station. This would allow local/stopping services from Bristol/Bath and from Trowbridge/Melksham to terminate at Chippenham and turn back. It would also keep the through platforms clear for freight and inter-city services, creating significant additional capacity.
This bay platform option would be far more affordable than reinstating the disused platform as a through platform as half the number of points and signals would be required. Local through-services to/from Swindon could still use the existing platforms but with two intercity services an hour in each direction stopping at Chippenham and Swindon, using Chippenham as an interchange may be a much better use of the capacity available on the network.