I believe that it is still Class 159 on SWR services. Only a few minor differences. Great suggestion though. If made it could also open the opportunity to build the North Downs Line from Reading to Redhill and Gatwick Airport as this would completely link up this suggestion with GWE and London Commuter.
elarthur You are right about the 159s. The 158s only run the Romsey - Salisbury and occasionally the Reading - Salisbury.