The thing is seL4 had (has?) many limitations which made it not very interesting for the real world: at some point it wasn't able to use multiple cores, or use

The thing is seL4 had (has?) many limitations which made it not very interesting for the real world: at some point it wasn't able to use multiple cores, or use low power states.. I think that only people who have closely looked at seL4 can tell whether it's really usable for their use case.