Twitter vs. Disqus

Additional metadata - a tweet could attach to a specific URL, which the URL owner could reject if needed. So, I could build a post form on my site to submit a tweet that shows as a comment, or you could use the API to attach a comment to my page, and I could accept or reject them as desired. Perhaps even have different rules for tweets posted from my form than from the API, etc.

Tweets don't have to be limited to 140 characters. I believe Twitter has kicked around the idea of longer ones. I'd personally be in favor of upping to 200-256 and then even allowing a paid tier (either monthly or per tweet) to go to longer lengths, attach more media, etc.