It's called common sense. There are no "red flags" unless you are trying desperately to find them. AMD has stated on plenty of occasions that Mantle is in it's very early stages.
It's common sense to have the biggest new feature of your first new line of cards in 2 years be unsupported by anything at launch? If that's the case, then I hope the saying, "common sense isn't so common", is true.
This is not a feature that AMD ALONE can implement. The dev has to do a major part of it, and the game isn't even released yet. So how is Mantle not launching immediately down to AMD's 'incompetence'?
It is incompetence on AMD's part to announce something like this just before the release of a new line of cards making it a clear attempt to increase sales and drum up excitement, when the fact is, nothing will support it for at least 2 months after launch. Not even a playable demo of something to give us an idea of what it can do?
Don't make an announcement like this, then let me spend $700 on a new card just to find a slip of paper in the box that says "IOU."