I think the most likely use case is to have this permission applicable only to a user's own card (and cards plussed with it). This lets me "own" my page and make my own addendum to any other card as a card, rather than a comment. Of course, then I'd want to be able to have one mechanism mean "read-only public, write-only rjbs" and another for "read-only rjbs." I'm not sure how yet.
I can see how it wouldn't fit perfectly with roles as they are, but a separate interface for doing this from the current (or setting-ized) permissions interface seems likely to be annoyingly redundant. What are your objections to doing it as a role?
Are you thinking a narrow solution around account (and related plus) cards, or did you have a more general solution in mind?
This change will come with setting-ize permissions, which will let you do everything we currently do with roles but will considerably reduce the magic of the "Role" cardtype. I'll spell this out elsewhere, but since the interface is going to be the sets/settings interface, it will be a very different situation.
I don't think we've entirely worked out how the author thing will work, but it's likely to be about syntax, not roles.
The current proposal in setting-ize permissions spells out the current plan, which does not really involve an Author role, per se, but addresses, I believe, the key user stories that prompted this ticket. closing for now.