You joke but one nice use of them is a simplified system interface which can allow a traditional OS to give such processes significantly lower privileges, e.g.

You joke but one nice use of them is a simplified system interface which can allow a traditional OS to give such processes significantly lower privileges, e.g. to sandbox something like mplayer. Unikernels make it possible to play with where you put a bunch of code that would otherwise need to be in the kernel or reimplemented.