That will never happen though. There will never be a "WYSIWYG" editor that handles just any custom BBCode. Those are better left as text in the editor.
At best it would be possible to match a subset of popular BBCodes (like center/align) to features that are already found in rich text editors. I believe that's what this extension does and that's the correct way to do it.
By the way, I need to clarify something I wrote in my previous post: I meant that this standard phpBB editor, that I am using right now composing this post, is boring. This WYSIWYG editor I like a lot.
The editor that allows adding custom BBCodes with gifs is Advanced BBCode Box.