By domains, do they mean that as "actually in use in certain sectors in the industry" or "a prototype has shown that"?
> causing some to propose that the days of Linux's dominance may be coming to an end
Who exactly would make that claim?
So, besides performance: what actual, real-life problems does this solve? I think there is some overlap with containers, and at this point, replacing them will require something a lot better.
Well, don't go jumping to "besides performance". Dennard scaling is dead, and the things that can interrupt your program in a full preemptive kernel system are myriad.
Furthermore, even if your application properly manages and produces backpressure, the OS can introduce buffering where you don't want it, often by necessity (to avoid massive context switch costs). Now, if you just want to manage backpressure over the network, an application-hosted networking stack is probably a fine solution, but if you want to accurately translate disk backpressure to network backpressure it gets more complicated.
There are heaps and heaps of ordinary programs written for preemptive systems that would see noticeable, tangible benefits to users if they were run instead on unikernels; but the main thing halting adoption is the inconvenience of adapting programs. I tried getting Capstan/OSv to work the other day and the documentation dragged me through several apparently-outdated methods of achieving the same thing, all of which failed in incomprehensible ways. Tooling for these things could use a lot of work.