Actually, this function is already available. Top of the website -> Messages -> Send a New Message. Start typing the recipient's username in the appropriate box and click on it when it appears.I'm thinking it might be too much, but also, where on a Chapter it says "by ___", maybe a way to PM or something like that for progression ideas (I noticed that 1 author asks for in comments) or editing/mistakes.
Wizardry I did not know, the "feed".