Have a look at Native Oberon and AOS, both desktop operating systems developed at Zurich's technical university.
They are done in GC enabled systems programming languages and were used both as desktop systems by the teachers, as well as to teach operating systems classes.
Quite nice desktop environments using strong typed languages, but offering a Smalltalk like user experience.
http://www.inf.ethz.ch/personal/wirth/books/ProjectOberon.pd...
https://www.ics.uci.edu/~franz/Site/pubs-pdf/BC03.pdf
http://www.ocp.inf.ethz.ch/wiki/Documentation/WindowManager
The problem with any systems programming language is that it is only used as such, if an OS vendor makes it the only way to do OS programming. Like Microsoft does with C++ or Apple with Objective-C.