'4' and '5' are both on the very top of my Discourse chat wishlist, but I don't think they're critical for a v1.0. If anything, '5' should come before '4'.
meta.discourse.org is the most natural place to test the prototype of such a chat (as we did with Babble), and the sub-community most amenable to chat in Meta is the #lounge (which I think should be expanded to include user types like serial contributors, but that's a different topic). And all we need for that is one chatroom. I hope we can agree that this is the MVP.
Will gladly talk through these other designs on the side though!
Agreed. Linking to tags could get hairy though so I think "all categories" and "individual categories" would be best for starters. DropBox's Zulip chat app has an interesting concept of "threaded group conversations", and it's not the scary kind of threading that we Discoursians despise:
I don't have a perfect solution in mind yet, but I definitely think this is a solvable problem. That being said, figuring out ways to incorporate tag/topic-specific discussions is "next-gen" territory as far as I'm concerned.
I think Facebook Messages is a great example of a chat/pm hybrid.
It's always the same conversation, but in different gears. And when a user is posting a series of uninterrupted replies, maybe we could automatically merge them together.
Discourse PMs are already super powerful; they're basically what I always wanted Google Wave to be. I'm not keen on adding a competing conversation stream into the mix. All we need is a few more "live" features built into PMs, like presence info and opt-in quick-reply.