Created a phurl, added some comments, confirmed that "Change Subscribers" and "Change Project Tags" are now available in the comment form.
One minor fix beyond @chad's note.
While we're here, you can also add:
That should make the "Quote Comment" action available from the dropdown on the right hand side of comments in the timeline correctly quote comments like this:
Without setQuoteRef(), the link to the comment won't populate (I think the text just falls back to something generic). You can test this by quoting a comment.