WYSIWYG editor as a replacement

Is it hard to implement a WYSIWYG editor in place of the current bbcode markdown post editor with live preview? I am really curious to know about this, I don’t mean a overly crammed up editor, just a normal WYSIWYG with bold italics smilies and underline options, ya also image upload and URL, I think around the same number of buttons as the current one.
@sam @codinghorror

Covered in more detail here (I searched for “WYSIWYG”):