Many high-throughput server architectures, like modern thread-per-core designs, already do all of their own thread scheduling in user space. Similarly, they tend to do their own storage I/O scheduling in user space as well, bypassing the kernel cache and sometimes the file system. Similar with networking.

For this type of software, which treats Linux as little more than a device driver, a unikernel looks pretty similar to how they already interact with a normal OS, so porting to a unikernel should be relatively straightforward. I think this is more the case that unikernels target.

Well, Nanos definitely does scheduling and it supports multiple threads. In this day/age you kind of have to. In fact we are at the tail end of removing our version of the BKL.