You're right that there is no perfect heuristic, but Google Glass wad real and real stuff was done.
If you've ever been near or caught up in the whirlwind of one of these hustle jobs, it's obvious and unmistakable that nothing is "actually happening." They're not failed attempts to do something, but successful attempts to appear to be doing something. They're cons.
Well, from my perspective, Google Glass was an immense failure. Yes, they made a product, but not one that was actually useful for anything. (Really, I asked every Glass owner I could find what they were using it for.) At the time I thought it obvious and unmistakable that nothing would actually come of it. Was Glass better because people fooled themselves into putting forth even more unnecessary effort? Or was it worse?
That's not my point, though. My point is that from the perspective of the investors these things look great because they are optimized to appear that way. They may look dumb or pointless to people from other perspectives, of course. But it's like one of those optical illusions that only works when you stand in a particular spot. Every company does this with their investors. Every company does it with their customers.
I also think the dividing line between con and regular company is not as clear as you make it to be. How many people do you know that have stories of working at companies where the executives have no clue? E.g., the charismatic but coked-up executive, or the VP Sales who promises entirely impossible things on a regular basis. Stories where things only worked out because actually clueful people worked hard and made it happen. Or at least made enough happen that checks got cashed and customers didn't actually sue. I know a bunch of those stories, and I'd bet you do too.
I could easily imagine that this was not an out-and-out scam, but just something moderately more fucked up than places I've seen end up doing quite well.
If you've ever been near or caught up in the whirlwind of one of these hustle jobs, it's obvious and unmistakable that nothing is "actually happening." They're not failed attempts to do something, but successful attempts to appear to be doing something. They're cons.