Sounds good to me. I still think we may want to spin off this BBCodeizer plugin into a new one with a different name and host it on github. Perhaps we could do that and share commit access? I think we've diverged from the original plugin enough to warrant it.
Also, keep in mind that we don't need to use simple_format or anything really. I haven't spent much time on this part of the app (just enough to get it working) and it sounds like you've done a lot of digging. So, if there's a better way to go about all of this, please go for it!