Much of the cloud/virtualization industry is actually built on exokernels; a hypervisor is basically the commercially-viable version of an exokernel. The unikernel movement is an attempt to revive the LibOS and use exokernels as they were originally designed (i.e. move OS abstractions into user-space and not have a whole OS running on top of an OS), but there've been several pragmatic barriers that've kept them from gaining all that much adoption.
I think I am mostly want to say to the advocate of a certain on machine first-level software infrastructure above hardware to feel more free to try to prove their technology is the best.
