Unfortunately, as with many things these days, there are just some many issues to overcome no matter how much the WSR would love to be providing a service to Taunton.
For example, if they should want to run a service into Taunton, they'll need to undertake a full safely case, hire in Mark 3 stock from somewhere, train up all of their operational staff that operate on the mainline to have a full
PTS▸ certificate, pay Network Rail for track access, pay a driver, guard and signalmen to cover any shifts that can't be covered by volunteers etc. etc. In short, it won't be cheap.
In the short-term I think WSR should concentrate on developing facilities at Norton Fitzwarren. Taunton Trading Estate has masses of land that could provide a road spur from Silk Mills Lane to this potential facility. Even with the recent housing development on the former Taunton Cider site, I think there is still room for this to be realised. Now that Silk Mills LC▸ has been bridged there would be little in the way of traffic problems to gain access to a potential WSR station at NFW. By having road access seperate from NFW village, you need not snarl up the narrow road past NFW's Co-Op and the chippy!
In the longer term a mainline Norton Fitzwarren Parkway (or name it Taunton Parkway) on the land currently occupied by Taunton Trading Estate could provide an interchange with the WSR, thus keeping WSR off the mainline into Taunton proper. This Parkway station could provide huge public transport benefits to the west of Taunton which has a large catchment area.
TLM
It would seem that the best solution ultimately would be a completely seperate 'Up Relief' into the up side bay at Taunton.