While you are working on Fediverse support, there is a quick feature that could be added to Ghost without requiring a full Fediverse stack.
It would be nice to have a field in the staff area to let authors enter its Fediverse username.
This field could be rendered in the author profile page as a meta link rel for me tag such as:
<link href="https://domain.com/@myauthorname" rel="me"/>
This would make it possible to support author verification on Mastodon side, which is a prerequisite to later be able to render the link to the author Mastodon when sharing the link on Mastodon 4.3.
On each article page a meta property for the author would have to be added as well, something like:
<meta property="fediverse:creator" content="myauthorname@domain.com" />
This would be a great first step to support the Fediverse.