I agree that Lua is probably accessible enough from a user’s perspective.
Take for instance some of our must popular plugins: kak-lsp, parinfer and kak-tree depend on Rust, connect.kak has an optional dependency on Crystal and kakboard depends on usually not pre-installed external tools for communicating with the clipboard. And nobody looks at these dependencies as a problem.
kak-lsp provides binaries in each release, which is what I use.
kak-tree I only use on my work computer because I didn’t want to install the rust toolchain on my home computer. Instead of
kakboard I have my own simple clipboard copy snippet tuned to what is available on the systems I use. Maybe I am not a typical user, but as you see dependencies affect my decisions as a user.
Like I said before, it is a trade-off between what the author wants to use and what the user is willing to install. I wouldn’t tell a plugin author what language to use, but they should expect that users having to install dependencies will affect their willingness to install a plugin, along with its expected usefulness. For specifically Lua though, if I want to try a plugin I would probably install Lua for it since it seems easy and small enough.