As long as there's Bash and Python support, Gentoo Prefix could as well. That's kind of the only things that are hard needed for Gentoo as Portage is written in

As long as there's Bash and Python support, Gentoo Prefix could as well. That's kind of the only things that are hard needed for Gentoo as Portage is written in Python and Ebuilds are Bash scripts. Bigger issue would be that the Fuchsia kernel likely isn't POSIX complete.