Hints to avatar the last airbender book 4?

I just got done watching avatar extras, the last episode. When Zuko asked his father where his mother is, a rumor alert popped up, saying that some people think this is a teaser for a 4th season. And you know, most rumor alerts that they put on there are true. So is there any other announcements for a season 4? and do you think they will make one? I read on Avatar wiki that there was a storyboard for when zuko finds his mother, but michael dante dimartino requested it be written out, but i couldnt find out why.