Services like Plugoo, mabber, meebome, wambo enable people to chat with you via a chat box on your blog, you chat back using your IM client. Similar services are normal chat boxes where you also have to chat in the same box (not via IM). You can even have a link to a chat box for every post, see 3bubbles.
When I saw the conversation post form for Tumblr, what I thought might happen is post level chatting, ie. the blog post itself is a chat box.
Every chat post would have a permalink and the chat can always be open like Zpeech. Some sort of chatter blogs, where the owner of the blog initiates the chat, kind of a mix between a blog and a forum, only synchronus or asynchronus chat.
Maybe the post could have a title and a description and then the chat begins.
This would be great for conferences, someone starts a topical chat post on their chat blog, and if others know about it they can join in…basically chat blogging.
Even better, every chat post could have a special ID, so everyone can chat from their own IM, you don’t actually have to visit the site.
This would be great for a blog where each post is an interview…hmm, I guess this would be real time blog posting, no such thing as a draft.
Or perhaps where people own their own chat blog, similar to a blog network like Sponit, instead a chat network.