Well, the spec says:
It’s the email address of the author of the item.
So, using anything else is not really an option. Moreover, the hash would be as worthless as the current no-reply address. Or did I miss something?
As I see it the purpose of the optional <author> field is to identify the author and to provide an email address that lets me contact the author. Due to privacy concerns that’s not really an option here. However, the first thing in the <description>field is the name of the author and a link to the user’s profile page. Isn’t that enough?