There are going to be an awful lot of people defaulting on their Toyota Prius PCP deals...
Just last week I went in a 2017 S Class uber. The guy had spent nearly £100k on this car in order to be able to provide an Uber Lux service. I dread to think what he’s going to do now.
Uber are not the only company in London to work for, besides, that UberLux driver may not rely solely on Uber for his income. He could be a personal chauffeur, possibly with his own operating licence (which TfL now hasn't renewed!), and own clients, and probably sub-contract from other firms as well, and drives for Uber for a bit of beer money when he's not busy with his own work.
This was the idea of Uber in the beginning when it was launched in London in 2012 - using existing chauffeurs to fill in their gaps during their down time, while passengers would get a luxury service, for not much more than a black taxi, and it would've remained a niche service as you mentioned earlier.
It's the standard UberX drivers in their Priuises who rely on Uber who will be the most worried, however as I said, there are other private hire companies to work for, though Uber does have it advantages of being flexible (no set shifts to adhere to, usually), no corrupt controllers giving good job to their mates (Uber jobs are supposedly dispatched to the nearest driver who's been waiting the longest), and Uber takes a cut from each fare (which makes sense for part time drivers), rather than paying a minicab office a fixed weekly rent/circuit fee, payable regardless whether they've got work or not.
I've no opinion whether Uber goes or not. It's one source of income out of many, though a good thing about Uber compared to other firms I sub-contract firm, is that they're fairly quick to pay, i.e. next week (they've no reason to hang onto your money anyway as the passenger's card is billed not long after the journey), compared to faffing about with invoices and getting paid weeks/month in arrears later with other firms.
As a passenger there are other firms to use, I used to use a local firm such as Parkers, or sometimes use Addison Lee, and they often e-mail discount codes, which makes it just as cheap as Uber anyway.