Yeah, I'd want a jail dockerfile system too, I just usually do them manually. Still, a way to run dockerfiles to build jails would be epic if you could make it work.
I used gentoo for a decade, I just can't afford the downtime if my workstation goes down, so it's debian with lxc workspaces for a while, but gentoo actually runs well under lxc.
Mostly every app expects its own distro, either debian or centos, few actually are agnostic, so getting them to run on gentoo was always more of a challenge than on raw debian/Ubuntu.