They have if not directly. He has stated not to worry there will be another TES. That's all that really needs to be said. There doesn't need to be any more information than that and they're smart for not providing anymore information.
Still, I have to disagree with you on that. Saying that there will be another Elder Scrolls does not mean that its currently being worked on. That statement could imply that the next one won't be released until 2020.
So yes, I agree that showing something - from whatever their project is - should not happen until its nearing a final build, if only to save people being disappointed with anything that may have changed in the interum.
But in the event that when their new project is announced, it's not TESV, to save many of us that disappointment, could we please refrain from posting things saying its confirmed to be in production if such comments are only based on a vague & ambiguous statement made in passing over a year ago?
Im a sceptic. I need evidence. And right now, we have only circumstancial evidence.
But honestly, I don't doubt that the game in development is TESV, I'm just wary of this speculation forum turning into a breeding ground for false information .