The forum replaces any url scheme that isn't http:// or ftp:// with http. Would be nice to use btsx: scheme. I think gamey started work on this, but might not be easy with this software.
Yes I started. It might or might not be that hard, the problem is packaging it into a proper package to install on other sites. Hacking something up on a single site is a lot easier. I have a site I'd like to test it on, but if this site is going to change soon I've been on the fence about starting it back up since I really haven't made any progress and don't know the SMF learning curve I will encounter. So when done, it would basically be aimed at me and the off chance we get theymos to accept... and maybe some other SMF sites. My site is just sorta meh, but if someone knows theymos and he is agreeable to the thought then it could add a lot of value to the project.
Actually if theymos agreed it'd be huge, but the plugin would have to be well written etc, and who knows if I can even hook into it system at a deep enough level without basically forking SMF.
edit - Although there is a SMF forum with some really helpful dude with 50k posts. Once I understand the btsx: protocol completely from the php prototype then I would start looking into SMF and those guys could be helpful in ascertaining the difficulty.