What Twitter needs is baked-in hashtags-as-chats, or, even better, the ability to do on-twitter chats w/o hashtags.  For example, I should be able to enter a twitter-based Mets chat pretty easily, (a) discovering other Mets fans and (b) not polluting my stream.

It could be done as a kludge pretty much immediately:

1. Participants in the chat would follow a hub account, such as @MetsTweets
2. Participants would also set up a search on any mentions of @MetsTweets
3. To send a tweet to the chat, you’d preface it with “@MetsTweets.” 

This would serve both purposes.  Anyone searching for “@MetsTweets” would see the Mets chat, and because only those people who (a) follow you and (b) follow @MetsTweets would see the tweets (absent a search), the tweets wouldn’t pollute my stream otherwise.

It’s not idea, though, because it requires the search tool, which doesn’t carry the ability to block with it.  For example, there’s one particular Mets fan who I’d rather not listen to, and I’d love to be able to filter out anything he says and is said to him.  I could set up a more robust search query which would allow for this, but that’s going beyond the “simple” solution.  Twitter would have to build better blocking tools, but if they’re going to do that, they as might as well build in the chat functionality.