I’m not sure residents in these areas would benefit much from this, considering that they are (bar Clapham) well connected with the London Underground which journey times are going to be just as long.
On another note, I’ve been reading through Farnborough Airport’s proposal to increase the number of flights in the future - namely in the pursuit of the business aviation sector, as flights would direct business travellers to Heathrow from Farnborough. If that’s not an argument to justify the Heathrow Southern link towards Basingstoke, so as to create modal shift among these business travellers to the railways, I don’t know what is.
Ok so I mentioned those main nodes because they are hubs/have feed. Not just residents. I didn't mention Feltham or Twickenham either in my previous post, also busy local hubs. Putney too, if it called. The train would be completely full.
Seccondly, the tube from those places to Heathrow is not amazing. Vauxhall misses the Elizabeth Line, so you're going Piccadilly via Hammersmith or Green Park. Waterloo gets to TCR - might be comparable. Richmond is a no-brainer, big outer centre, feed from NLL/District, especially poignant if OOC NLL doesn't happen... plus also feed on the line itself from Putney, Wandsworth, Feltham (would have calls) - etc. It doesn't compete with EL at all, it's wildly complementary.
And as for Clapham Junction, that alone might fill the train. Look how many use it for Gatwick. A clue - nearly as many as Victoria and way more than LB. The Southern network (and LO ELL) would feed that service too. Much faster than going up to Farringdon (for BML people).
And it's amusing you can decry this, but then think a few more private jets from Farnborough either justify a rail link there, or would cannibalize LHR! Not even apples to any type of fruit...