442s are the best third rail train ever built.
HSTs should be fully rebuilt and upgraded and made to serve another 40 years, with all SSL units to be returned to CrossCountry duties, replacing Voyagers.
458s should be subject to the same rebuild.
TfL's A stock should have gotten the D-train treatment.
Thin, upright seats were made by a sadist and should be removed from all rolling stock and replaced with something much more comfortable.
First class should be reservation only and over-21 only (both already mentioned in this thread). Complimentary drinks and nibbles should be available to all first class passengers, with a proper catering service available on long journeys. The guard will throw you out if you're loud and obnoxious.
Reservations, regardless of class, should be chargeable. (already mentioned)
Football trains and late night trains should have at least one carriage which has tread-plate stainless steel floors, New York style subway seats, and grab handles, for the drunks and rowdy idiots to use. The sober, quieter people will be permitted into a regular standard class carriage. These trains will be dry.
Where toilets are not provided on trains, stations that are only served by those trains should have a toilet on each platform.
158s should be reformed into four carriage units, 159s into fives, with a new batch of carriages to be made (without cabs) as necessary. The interiors should be built to SWT standards. They can then stay on their existing routes.
Voyagers should be completely gutted and rebuilt with higher quality materials and more comfortable seats.
Make the Lymington Branch more useful by extending it to Southampton Central on an all stations pattern.
Bring back BR, NSE and Intercity and their liveries at the time of privatisation - i.e., nationalise the lot. Have more regions, but have the regions answerable to the councils in the areas they serve first, government second.
Build a Japanese style high speed intercity rail network that is mostly isolated from other rail services. Brand it Intercity and have it call at cities and large towns only. No level crossings, no bridges so people can throw things onto the track.
Not very controversial, I guess.