- Portability: it's just as portable as lxc, so if you meant portability in the sense of 'well he could use it on FreeBSD if he wants to switch from Linux' I don't think there's a win there. If you mean that his containers won't depend on the environment used to spawn them, I guess I don't think that's so important. I always make sure my environments are easily reproducible, and I am happy to reap the reward of that--the reward being that I can do 'unportable' things and not have to worry. Instead of running the environment you want in a container, why not just run it normally and skip that step?

- Reproducibility: see last point. If he wants reproducibility, he can shove that one-liner in a script somewhere and call it.

All he wants to do is isolate a process. You don't need a chroot for that, or service discovery, or lifecycle managment, or a Dockerfile, or whatever else. It's like if someone advocated the use of a 'grep manager' instead of just running grep. The simplest possible thing to do is unshare the namespaces he wants to isolate from harm. So I suggested exactly that.

EDIT: also re portability, it sounds like the rest of his environment depends on these Python scripts anyway, so I don't think he'd gain anything from being able to use them in a different environment.