The way this works is that if there's a "${HOME}/.myzshrc.local.zsh"
it is sourced and does some machine-specific adjustments that are not
contained in the general .zshrc file. That local script can also set
local_plugins to a list with plugins that I only want/need on that
machine (e.g., a plugin to work with the SLURM job scheduler on an HPC
system).
I am doing something similar but with simple conditionals in .zshrc to test which machine I'm on and load the appropriate plugins. So far my config is simple enough that I can get away with it but I can see where if it grows in complexity, your method is a lot cleaner. I'll definitely keep your setup in mind and refer to it later is I my config gets unmanageable. Thanks!