For that I wrote a small plugin. I used for that the ckeditor, it works for me. And yes I know it is not 100% done, there are some small issues inside. Maybe someone from you can help me to fix that.
Still now, my major problem is the .htaccess. That the ckeditor is working I have to include js files, but in the .htaccess is this rule.
RewriteRule ^site/(.*) error [R=301,L]
I need an exception for โ/site/fields/ckeditor/assets/js/*โ
by the way - funny is that most of all kirbytags are working.
As far as I know it should be possible to include the js files in the assets in your ckeditor.php, you may want to have a look at the color picker field (https://github.com/ian-cox/Kirby-Color-Picker) or similar for how to do that.