is Da Man really gonna make a 'Chang Username' thing in the summer?

Well, it says so in his signature, and I doubt that he'd lie. :l

As Jeffrey said it does say in his signature. However I think it will be like the gradient a-z where only certain people can get it. I.e people who start off with inappropriate nicknames that need to be changed, and probably people that win the right to do so. But as I said I do not know for sure.

There is a possibility.

But, the game needs to be re-coded so that the username changer feature can change your usernames easily without causing any new glitches to occur.
You just have to wait and see what will happen in the summer.