Perhaps for something that was embedded (like an OS for ARM microcontrollers or something), but a desktop or server OS is unrealistic.
The problem is drivers - unless you manage to port Linux drivers or something to your OS, it's never going to be able to use more than an extremely narrow cross-section of hardware.
It very good for the educational value though! Making a kernel that boots a simple shell, and eventually runs statically linked executables is possible in a few months if you spend a lot of time on it (and a lot of that time is research, not coding).
The problem is drivers - unless you manage to port Linux drivers or something to your OS, it's never going to be able to use more than an extremely narrow cross-section of hardware.
It very good for the educational value though! Making a kernel that boots a simple shell, and eventually runs statically linked executables is possible in a few months if you spend a lot of time on it (and a lot of that time is research, not coding).