Are there any plans to develop Wolfram OS?
Google has developed Chrome OS/Chromium OS
dedicated to easy and fast access to the web.
Valve has developed Steam OS
that created primarily for playing video games and provide huge performance boost because of tight integration of the OS with a computer's hardware.
Both of the OS's are delivered as pre-installed OS on the special machines such as Chromebooks and Valve Machines.
Since Mathematica is "integrated all-in-one platform", there can be a lot of benefits to have own OS - Wolfram OS that can be the defacto platform for computations and research and provide significant performance improvements over the standard OS's. I think a lot of hardware manufacturers will be interested in delivering scientific-oriented computers - Wolfram Machines.