As far as end user devices go, it's a mature industry now. Once a certain level of functionality has been achieved, the devices become more polished but also more locked down. Happened to things like cars, stereos and others before. I bet full self driving cars will be completely sealed and no tinkering or self repair possible. They will be as or less repairable as an iPad.

Developer machines will probably soon be viewed as specialized devices that most normal users will not even know how to use.

This is mostly ok. Most end users don't want or need general computing.