"Electrification to Salisbury" seems to crop up on here as often as "moar HSTs for XC" and "My Idea For Future Uses For Some 1970s/1980s Trains".
The way I see it (as someone living in Yorkshire, who was last in Salisbury before the Russians made it trendy), SWT ran a slightly messy service with a slightly messy assortment of two/three coach 158/159s - they were able to expand the fleet a little and use the "weakness" of the relatively short trains (compared to the rest of the SWT fleet) as a "strength" and make various incremental improvements (effectively running a half hourly Yeovil service in the direction of the peak flow, extensions towards Bristol/ Weymouth).
Making the best of the units they inherited was admirable but if you started speccing new stock for the line you probably wouldn't order pure diesels, you probably wouldn't order such short units, you probably wouldn't order 90mph stock and you might not even order 23m long coaches (given that the
majority of the SWT/SWR franchise is electric, 100mph, four coach minimum and generally 20m coaches).
It's the difference between Ready Steady Cook (cobble together the best you can with the ingredients that someone else has selected) and Masterchef (chose the ingredients yourself and then cook something with them).
If you assume that electrification isn't going to happen any time soon then you'd have to have a serious discussion about exactly what you are planning.
158/159s are one thing - you can plan to get your hands on cascaded ones from other TOCs to expand operations - but if you are ordering bespoke stock then you need to be sure exactly how many you need and what you plan to provide over the next generation.
- Is this a direct replacement for the existing frequencies?
- Are you planning on expansion?
- Should you replace the short trains and all the required joining/splitting with longer trains that don't require as much portion-work (but are less flexible)?
- Can all of the "local" stations cope with something longer than a 158/159?
- Are you giving up on any ambitions to run a Waterloo - Okehampton - Plymouth service?
- Is Waterloo - Bristol continuing as a long term service?
- Are you focussing on passengers east of Salisbury or longer distance ones (in terms of seating, doors etc)?
- If we are moving away from "private" franchises to a "publicly owned" unified railway then do we forget about using the Salisbury route as a "cheap and cheerful" alternative to the full price B&H route? (i.e. we only plan for intermediate passengers, or are you going to keep some seating to keep competing with the parallel service from London?)
- If we expect passenger numbers to bounce back towards pre-Covid levels then presumably you want to be able to fill platform space at Waterloo etc (and not have it taken up by a locomotive)?
Plus there's the issue of whether ordering something "bespoke" for the Waterloo services means doing the same for the "Salisbury 6" routes or leaving that as a relatively small fleet of pure-DMUs within the SWR operation? Passing it to the GWR operation?
Thankfully the 158/159s don't need replacing right now, so there's plenty time to take a longer term approach to what stock runs the route in the future (rather than being bounced into ordering something off the shelf like 195s). It's going to be over a hundred carriages so you should be able to order something suited to the Salisbury route in the 2030s/2040s/2050s. Maybe by then the technology will have changed a bit from today's developments - remember what people were worrying about the 800/801s five years ago - a lot can change.