Presumably you mean sales of cheap phones couldn't be supported as there would be less demand.
So it seems like new sales would be hit but in favour of second hand phones? That seems like the right thing - more use of products that can be repaired and maintained for longer is good, right?
Second hand phones are a shit-show, full of hidden costs (often at least new batteries and paying to check if it has been stolen) and people treat their phones like crap, meaning once the often one-month warrently you often get will not matter much once the phone starts bootlooping after three months from damage caused by the last owner.
Good luck proving that the last owner dropping the phone over and over caused the bootlooping and you would have to spend more than the cost of the device to take someone to court.
Poor people de-facto don't have those legal rights, only what the seller is willing to allow.
If it happens in the first 6 months, you don't have to prove it, the seller has to prove you did something to cause the bootloop[1] (and it's usually not worth it to them). I've had good luck with warranty claims beyond the 6 month period, when sticking to reputable sellers.
I mean the cost of the phones would obviously rise if their manufacturers are to do what this proposal dictates. For cheap smartphones the increase will be the most dramatic.
This is how it should have been. Who needs a cheap phone which is obsolete after 6 months... If you need a burner phone you can easily buy a dumbphone. The problem is manufacturers like Xiaomi are misleading customers into thinking that their devices will last them for years.
There are many more models of low-end phones than high-end phones. Manufacturers could adapt by producing fewer models of low-end phones, which would make them less expensive to support.
