I call BS until we get an official update. The likelihood of jigglypuff getting back in actually may work, but the portrait looks more like Pokemon Trainer than Ness. Look at the hair style and the hat.
Edit:Never mind I just noticed the other portrait you were referring to.
Ness would have to be given a completely new move set, and seeing as how the way the Lucas update was worded, it seemed very likely that Ness was replaced.
The Lucario portrait is questionable since it's kind of hard to make out. and also I'd think we would have seen at least the announcement of any of those characters by now, especially since the Veterans section needs an addition badly.
I'd like to think this rumor is true but I'll take it with a grain of salt and settle on: We'll see.