Doing some research on operating systems design you can choose the kernel model and in this case you can expect that microkernel is more stable, powerful and flexible compairing with monolithic design, exokernels are too platform specific and more complicable for application level platforms (i.e. embedded systems with too limited functionality). But like a bonus you will got the new area of research in this area - choosing and developing an instruments for implementation.
On this area, in my opinion, are old and good instrument is a pure C language for microkernel, for low level. But in case of many reasons C development has a long time for something bigger than microkernel, for microkernel you can extend C with macros or write your own preproccessor to extend C (like my project extC). This is good and right, but for microkernel servers and user level is better to use something else, more powerful with paradigms and more easy to develop.
It's not C++, not only in case of my hate to pluses, there are no reason to use C++ in any kind of development, C++ contain many ugly stuff and it has an ugly design overally. There are ObjectiveC, but this language will not decide our wishes.
I'm looking to functional programming languages - this way is more powerfull, well-designed lisp-like language is really simple to implement, they all has a simple syntax - and learning didn't takes a long time - it's intended to be meta-level development.
With its powerful I'm thinking about crazy things - what about to design a several DSL that can be simply implemented on Lisp/Scheme/Haskell , for different types of microkernel servers.
In example, you can research for often used language features and constructions that required for implement a filesystem, or block device driver, or network device driver etc...
I'm thinking to go deeper in this area after MuiString will ran. I promise to make a deep research, implement expiremental DSLs for this purposes and test it for perfomance and other things.
Be updated, take a look to functional programming of your research - it's a wonderful world of new features and paradigms.