• People who put OpenGraph tags into web pages are not necessarily developers themselves, e.g. WordPress users who are putting information into a plugin UI, or editing an existing theme
• ActivityPub URIs can be ambigous from the user's perspective, for example, the "pretty" URL that shows the web version might not be the URI, in some software the URI uses a numeric ID (or UUID) of the account instead of the username, from which you can not gleam which account it refers to at a glance.
• Typing username@domain when composing to refer to accounts is predominant on the fediverse, most people who put their fediverse account in promotional material (e.g. event flyers etc) also use this convention instead of using an ActivityPub URI, so it is very familiar to most people.

Unfortunately, because this FEP describes a feature that is already out there in the wild, there's not much we can change about this without breaking compatibility with existing websites. At best, we could say the value could be the Webfinger handle or the ActivityPub URI.

The content attribute is to contain the WebFinger handle of the author's fediverse profile, i.e. username and domain separated by an @-symbol. A leading @ can be included and ignored when processing. This format was chosen for its user-friendliness, as this style of handle is what users would be used to seeing and typing when using most fediverse software.

This choice was criticized a lot when the feature was introduced. Meta tags are primarily read by machines, not humans, so user-friendliness shouldn't be a concern. Reliability, on the other hand, is worth taking into consideration. preferredUsername and the user part of a handle can be changed at any time. Actor ID is a more stable identifier and in my opinion is a better match for the fediverse:creator tag.

I'm thinking of the case where we would rather have the linking site/instance embed the content as a quote. As more websites should become ActivityPub enabled or aware this seems like a solution for a transition period. I hope.

Thank you for the time of putting it down to paper though! And we will definitely look for a proper place to apply it in the meantime since the actual reality of the matter is, not everyone is ready for it yet.