I completely disagree and will forever disagree on everything which affects WYSIWYG.
Specially what affects JavaScript-based WYSIWYG editor. During many years of programming experience I've never met more bugs than in such tools, and more bugs are to come with each new version of the browser or even with the new browser released. Additionally, such editors restrict usage of forum functions like highlight-quoting, username insertion, or smilies pasted via add-on and many other additional premium functions like Polls, additional BB-codes and so on.
It is much affordable solution to keep the clear textarea else to oveload it with the sh*t like you suggest.
I know many of my customers and many users will support me in this case (since I know many customers were specially asking me not to embed WYSIWYG into CMS or other kind of form I worked on for them), so I must disappoint you: it will be never implemented in miniBB. Or it won't be implemented at least this thing works absolutely in all browsers, and it's not the JavaScript-based, but embedded directly into the browser and supports all native functions which can replace BB codes. I think it's almost impossible even in 2050 ;-)
You may check this threads for more:
WYSIWYG - in forum's posting message area