I've thought about this and I'll be damned if I can't think of a single example. The closest I can come is some of the old steam engine tech, where they would have a huge public competition and one demo engine would be crazy fast, but the hype was never at these levels.
Basically, as a student of business history of sorts, just considering the base rates for these situations, I'd be willing to give generous odds that Magic Leap absolutely fails to deliver anything worthwhile. It just doesn't seem to happen. The true breakthroughs are built by those quietly plugging away, scared to death that if they take a breath to talk about it their competitors lurking in the shadows will pull ahead.
It really makes me wonder who these investors are that piled on. The first $100M or so I understand; they thought they were getting in on something new and great. But the next $1B? Did they never read a business history book during their MBA program?