One thing I'm cautiously watching is NixBSD. With nix you can trivially compile all your software from source and modify it (both of which I do on the Linux-based NixOS). So I think that would cover the main selling point of Gentoo, though naturally it adds the Nix layer that you may either love or hate. The only reason I haven't dived into it yet is my FreeBSD machines are all foundational parts of my infrastructure so I don't want to take a gamble on such a young project. So for now I just load it up into a virtual machine and poke at it longingly from time to time.

https://github.com/nix-community/nixbsd