> E.g. by opening up the bootloader and letting users install custom software.
If limited to the bootloader, such as allowing users to run their own operating system, then that is definitely a possibility, with the exception of firmware running on the device itself. But I doubt that is what most users here are expecting, and in my opinion, it wouldn't provide much value to the vast majority of customers.
It would open up a tertiary market for smaller companies to do that (maybe even sell into a different market).
Not every business venue needs to be a multi billion multi national and using some devices for a long time is better than burrying them all in a land fill.