I wanted to get an initial version out the door, so I have deferred going with this heavy-weight route, and opted for having the user enter a string of JSON to configure the supported kaomoji replacements. It’s clunky, but it works.
In any case, I have the plugin live on my server now. You can find it here. I welcome any feedback. I’m a web, Rails, and Discourse newb, so I’m eager to learn. I did my best to ape the practices of other popular plugins. Thanks for your help.