Re-posting from the Discord
I think a similar experience to vscode extensions, but simplified, might be quite a good way to solve this problem. I can imagine an extensions page that allows you to easily add and remove extensions from your Kagi experience.
To keep things simple and relatively easy to implement these extensions could be simple JSON files that live in a public GitHub repository. Depending on how flexible the JSON format is this could handle themes, bangs, filters, and many more parts of the Kagi experience.
In addition to this I also quite like the idea of "meta" extensions which are just a list of extensions to install. This would allow members to share their entire Kagi configuration with the community, or even allow people to share a combination of extensions that are useful for a specific use-case.