Spooonky adding the opt-out feature is a bit complicated with the current extension.
The easiest would probably be a global opt-out, where the user can refuse all emails from the extension. That's maybe 1-2 hours of work. If we want to add an option for admins to bypass the opt-out when sending an email, maybe 15-30min more work.
What I'd really like to do is a proper newsletter extension, so that users can opt in and out of various lists and admins can track who is subscribed to what. But this will be tens of hours of work, so that's not happening before next year.
Adding support for HTML is complicated as well because a lot of testing will be necessary. Might be 2 hours of work or more, and would still just be copy-pasting of a full email HTML, not a visual editor. I would probably need to implement some sort of variable injection system so you can get access to the opt out URL and the username/display name from inside a custom template, because I don't see how I could automatically merge this together without an advanced templating system.
You can contact me via the email on my website or on Discord if you'd like to move forward with those features. I don't think I'll be able to work on it before next year.
