I don't know if coding a bridge is particular hard for Joomla, but XenForo-Joomla bridges tend to get abandoned very fast. Perhaps it's because people say Joomla sucks. Well I tried WordPress and I don't like it. You have to dig too much through php files to achieve something that would require zero php file digging with Joomla. Once you understand how Joomla works, you will learn to like it.
Anyway, is anyone willing to take the challenge to make a Joomla (2.5) bridge with the same features as this?