The main value seems to be as a research vehicle and teaching tool rather than production-ready infrastructure. The Rust version being archived suggests this might not be under active development currently.

Good for simple stateless services (web servers, API endpoints, microservices) applications that fit the unikernel model - single-purpose, statically linked Running on one's own Xen hypervisor infrastructure.

It reminds me of the old OSKit project from the Univ of Utah, which was also developed for research and teaching.

https://www-old.cs.utah.edu/flux/oskit/

I would argue that stateful services (databases, message queues, CDNs) all perfectly fit the unikernel model. The question is whether the additional engineering effort and system design is worth the performance gain.