one of the first things brompton riders do is upgrade the awful little wheels that are fitted for rolling.
"Bromton riders" do that? really? Out of 100 more less actual Bromptons, how many have fitted 3rd party wheels? How many of those who changed them did change them for bigger ones? How many because of better rolling needs? How many because of bling? I suspect a tiny fraction changed and almost none for functional reasons based on own experiences.
As you speak of "awful little wheels": Is it possible that you did not recognize that Brompton has changed the standard roller wheels already back in 2015 - seven years ago? Is it posiible that you did not recognize that since the early 2000s the "easy wheels" were available directly from Brompton as an upgrade? Are you one of those, who, based on 20 year old experiences, today actively talks people into "upgrading to easy wheels" in ignorance that the actual wheels exist in the first hand and - depending on what aspects are important to you - are either better than the easy wheels or at least almost as good?
Swiftly followed by the equally grim folding handles.
I do own a bunch of Bromptons. One has folding handles that differ from standard - Eerdermetal ones. They were on the bike when I bought it used (and they are indeed better than factory standard). I do barely see 3rd party handles on the street and the people that have changed to 3rd party handles (apart from the Eerder ones) have done it for the optics - typically they even say they handle worse, but they look better.
That's true.
I won't bang on about the other upgrades possible.
Would be interesting. I have the suspicion that if back then when approaching Brompton with your idea of a tuning department they may not have liked your attitude and communication style but way more important: What you have in mind may be a market (and Brompton serve it themselves - they do have a small amount of "blingy" upgrade parts including handles since I think last year) but it it not at all relevant for the mission of the company which is about changing urban transport. So maybe you were too early, maybe you were too nasty, maybe your concept was not convincing to them, maybe your vision was not their vision.
If it was such a great idea: Why didn't you start your own business then and produce that kind of stuff? I you were right back then you would be a rich man by now...