I suspect the main advantage that the Unix family has in targeting these smaller environments is more the user-space than the kernel - init, the shell, the contents of /bin and so on.
It's pretty easy to configure a minimal but useful unix system without needing a GUI, graphics drivers, GUI configuration tools and user interface toolkits - look at one of the Linux-based router firmwares like DD-WRT for example. I don't think the existing windows user-space can be shrunk to fit on these small platforms, and if Microsoft built a new user-space to run on an NT kernel they would lose the developer familiarity that is probably the main selling point in the first place.
I don't think the existing windows user-space can be shrunk to fit on these small platforms
You should take a look at Windows Server Core Edition. It has enough of a GUI to run Notepad and CMD.EXE and that's it. Everything else is done remotely.
It's pretty easy to configure a minimal but useful unix system without needing a GUI, graphics drivers, GUI configuration tools and user interface toolkits - look at one of the Linux-based router firmwares like DD-WRT for example. I don't think the existing windows user-space can be shrunk to fit on these small platforms, and if Microsoft built a new user-space to run on an NT kernel they would lose the developer familiarity that is probably the main selling point in the first place.