Currently you can only be alerted when someone either quotes you or replies to the thread. Alert me when someone REPLIES to my message even without quoting it.
You aren't talking about the same thing as Marcus, I don't think. Either that or I misunderstood him. Of course there's a way to track who responded to you and what post they responded to if they're clicking something in your post - reply, quote, whatever.I participate in the Compuserve/Netscape forums. They are not threaded. They are not even based on threading technology. But they are able to track who a message is written to. And I get an email with a link whenever someone replies to one of my messages. As for how technically difficult this is, it looks pretty simple to me. If xenoforo knows which message to quote when you press the reply button, it is not a big leap to also know the message number and who wrote that message.
Personally, I think it's worth considering.