I do see what you mean but asking people to re-write all the things isn't a successful strategy to achieve mass adoption.

Being able to build your unikernel (micro)services using legacy things and then swapping out certain services for clean-slate versions seems like a much more palatable approach. This is why unikernels fit so well with the microservices approach — you only have to re-write things one piece at a time if you choose to.