Currently, a chunk of this route (St Deny's to Bournemouth) is already available as a route, but I'd love to see this extended out to the entire line. Even just to have the Waterloo to St. Deny's bit would be great.
I can see them doing it in future, however seeing how waterloo to portsmouth only came out a year or so ago, i doubt it's a top priority.
I would love for the section between Woking at Southampton to be done along the SWML so we have the primary mainline for most the route without a break. It currently just feels like there's missing piece just waiting to be filled.
The original PDL has a network of track and basic geography radiating from Woking and Guildford in all directions. AFAIK the Waterloo-Portsmouth used the old PDL as a base so future extensions are possible.