• You’d have a lot of scams / lies where someone is accused of doing something they don’t remember doing, they wouldn’t know whether they did it, and third parties wouldn’t be able to evaluate reactions / cross examine the accused.
• You’d have large corporations demanding that ex-employees forget everything proprietary, even if that would prevent you from building up skills in your career.

You’d be surprised what a small team at a large corporation will do if it lets them complete a project within budget. The PlayStation 3 originally allowed users to install custom operating systems. A lot of groups, even the US military, bought thousands of them because they were inexpensive computers (sold at a loss) and used them for compute projects. Sony eventually stripped out the functionality in an update, presumably because they wanted to cut out this type of buyer.

Yes; it’s pretty trivial to flash something like OpenWRT on them as they don’t restrict what you can install whatsoever.

You can basically do anything in OpenWRT, and if my memory is right a mesh setup is possible too. It may not be easy to setup, but it’s possible.