a future where all computing/devices are locked down

And who would mandate and control such a requirement? And how would it be enforced? And why?

The only reason Apple is locked down as it is, is that Apple as the only manufacturer has absolute control over architecture, hardware and software.

Being open will always be a unique selling point by at least some competing companies, so there will continue to be some, absent a dictatorship rigorously controlling the manufacture and sale of such devices. But I think not even China has managed to accomplish that. Open devices are an absolute necessity if you want research and technological progress. And if the industry needs it, some of it will inevitably become available to citizens, too.