One of the most useful ideas behind rump kernels, from what I can see, is as a technique rather than an end result: it's a great example of how filesystem drive

One of the most useful ideas behind rump kernels, from what I can see, is as a technique rather than an end result: it's a great example of how filesystem drivers or other typically privileged code can be reused in a lesser privileged context or even across operating systems and/or architectures, with minimal effort. This seems like mostly speculation on a mailing list, but I believe it's worth pointing out that this speculation doesn't do justice to what rump kernels can already offer. It would be nice to see other OS developers push models like this, to facilitate code reuse in widely varying contexts, instead of just "hypervisors".