I used to be in the unikernel camp of "this is the next step in virtualization tech", but having played around with both containers and unikernels, and now developing with containers, I think unikernels are going to occupy only a very niche space.

There are two touted benefits of unikernels, performance and security. Performance turns out to be a red herring, as the overhead of an OS vs a Hypervisor turns out to be roughly equivalent (with the OS actually winning in some use cases).

Security is definitely an issue, but it's so abstract. My company is a compliance (a very specific industry's compliance) cloud provider and we have gone with Docker as we get to use the OS as our Hypervisor, which means it is much more extensible and, in our use case, secure as we are able to auto-encrypt all network traffic coming out of the hosts with a tap/tun virtual device.

Two things need to happen to make unikernels attractive. A new Hypervisor needs to get made, one that is just as extensible as an OS around the isolated primitives. It should also have something extra too (like the ability to fine tune resource management better than an OS can). Secondly a user friendly mechanism like Docker needs to happen.