The Setup – Bjarne Stroustrup

"Able to act as an interface to other systems" is a matter of network transparency and authenticating to a remote node manager. Example: drawterm(8).

"Simple and predictable to use" is subjective, but generally lends itself well to systems built around exploiting a few Grand Abstractions to compose higher functionality. Inferno, Spring, etc.

"Stable, never needs rebooting" is already the case for big iron and mainframe systems, among plenty of standard microcomputer server racks. Microkernel architectures with autorestarting of failed drivers and well-defined communication boundaries greatly aid availability and reliability. The more important thing besides never rebooting is maintaining orthogonal persistence with frequent checkpoints so that rebooting isn't a big deal when it finally happens.