So here’s my idea. Besides reblogging, introduce a new feature I’d call ‘replyblog’. Themes could nicely show the fact that it’s a reply, just like I did in my themes when a post is a reblog, for example. It could also be reflected in the notes so that others will see that an entry has replies in the form of entries on other tumblelogs. New and exciting social interaction on Tumblr!
Isn’t this a reinvention of Trackback — but with the added walled garden of Tumblr?