Importance: 5/10
Problem:
The functionality to download a plugin and mod using a direct download link/URL to the .jar is missing. This functionality would allow us to install plugins easily that are outside of the known platforms such as Bukkit, Spigot, Modrinth and CurseForge (GitHub too, but that's for open source projects in general).
Solution:
Add a command to install a plugin and mod using an URL directly, and throw an error if the downloading file from the URL doesn't end in .jar.