True, you can design a CPU for anything. However a OS that depends on such a CPU is not portable to anything else, and can't easily run most programs that people depend on (emulators are possible, but not easy). Also most CPU advances haven't gone into such a thing and it is tricky to apply those advances while also providing what the language needs. None of this is impossible, but it makes such CPUs in todays world of questionable value.
Note that you can port any OS written in C to such a CPU with "just" a new compiler backend and a few drivers. Your OS won't take advantage of the features the CPU provides, but it will work.
Note that you can port any OS written in C to such a CPU with "just" a new compiler backend and a few drivers. Your OS won't take advantage of the features the CPU provides, but it will work.