A lot has happened in our work on standardizing federation with the W3C Social Working Group. ActivityPub is nearing Candidate Recommendation stage (we are aiming to reach that by October 11th), and in order to get there, we need public feedback! Here's a mailing list post explaining how you can help, though in summary:

Reply to this thread!
File issues on the issue tracker
Email Chris Webber, personally (though know that I'll be putting your comments publicly on the social working group wiki, though you can be anonymous if you like): send to cwebber AT dustycloud DOT org, with "ActivityPub" somewhere in the subject.
Send to the public-socialweb-comments list

Thank you! Your feedback is greatly appreciated! Here's to an interoperable federated social web!

Please note: The link to the editor's draft has changed. It's now here. Thanks!