Okay, but now you’re sending out lots and lots and looots of notifications via Twitter. Because unless you notify your users about replies to their posts or watched topics, they’ll be using their email client or webbrowser when they eventually see these notifications and won’t need to use Twitter to reply.
You do realize that everything you post on Twitter is completely public, right?
And the privacy issue aside, this is not what Discourse is about. It’s about being a platform for a meaningful discussion. And meaningful discussions are not to be had in 140 characters less recipient’s nickname and hashtag…