Given what you've described, I think you might be interested to look further at Irmin [1]. It's not quite ready for prime-time but certainly stable enough to kick the tires.

Regarding commercial uptake, the nice thing about the library approach is that companies get to pick and choose the components they want (without even going 'full Unikernel'). For example, I'm aware of the cohttp library having commercial users. The real issue is legacy code but I mostly sidestep that when I write (but we're well aware of it).

Interesting that you mention MirageOS in containers. I don't see any reason the two can't be compatible but it would good to hear more about what you'd like to achieve (or how you'd expect it to be in terms of workflow).

[1] http://openmirage.org/blog/introducing-irmin (I think it's time we put together an overview page with all the links).