thanks for your in depth comment and idea!
Currentl hellexis and I join forces to work together on a new/reworked mastodon plugin.
We base our work on the mastodon share plugin. Because of that, this plugin is currently only in bugfix/maintainance mode and will be deprecated in the end of April.
Please have a look on helixes plugin https://de.wordpress.org/plugins/wp-mastodon-share/ as that one is the one we will continue. It gives you a better possibility to configure the post.