It may have started with a mobile app, and he found some tangential success with printing name badges at conferences. But nowhere in your response addresses that maybe the OP didn't want to print name badges for a living. He sold his company which he wasn't truly passionate about which enabled him to do something he was passionate about. Sounds like a success story to me.
Not everyone's motivations are the same, and when that's the case we end up with criticisms that aren't focused on the essence of what is being told.
That said it's always hard to criticize success. It's like these guys just did a gymnastics routine and got a 9.5 and then we harp that they should have gotten a 10, while we sit here gobbling popcorn from the couch. :)
It would have been just as valid to stick with the idea people begged for/made money and add features that made you happy. Wouldn't it have been valuable to test/market View to thousands of customers with the need they were trying to solve?
I haven't suggested they should have stuck with label printing or that they should have sold it and started something new; my advice applies no matter what path they chose. I suggested that I don't think they learned the lessons that the market was willing to teach them.
In my wizened old age, I think back on similar situations in my own life, where I missed the signs and missed opportunities that would have had very low costs and very high pay outs. This is one of them for this team.
Since everyone wants me to have actually made recommendations for what they should have done (rather than what lessons they should have learned, which is all I covered to start with):
1. When you have a business that takes off on a run like this, and you know you're going to cash out and run; raise your prices. Raise them a lot. Double them. If volume doesn't drop, double them again. Rinse and repeat until you have found the point at which customers stop coming to you. Conferences are huge cash cows. They have money; if you solve one of their problems in a cool, social, way, they will pay for it. So, OP should have started charging earlier and more (a lot more).
2. Learn from failure. It sounds to me like they're back on the same sort of project as the one they couldn't convince people to like to start with. If they're passionate about social mobile apps, that's fine. But, you have to be willing to listen when the market says "We do not want this."
And, let's add a bonus third point:
3. Leverage past successes to enable future successes. As you note, it sounds like View could have been launched as a cool feature of the label business, getting it into the hands of all of those CEOs and investors that passed through their system. It started as a marketing ploy, and it would have been an effective one for the new product...I don't know that it makes the new product any more awesome or wanted by people, but it is still a valid avenue for marketing the product to thought leaders.
My point is merely that I don't think they really learned all the lessons they could have learned from these experiences. I'm almost certain they undervalued their label printing business, for instance. Certainly they should have started charging for the service earlier.
And, I also think that they're maybe underestimating the value of listening when the market speaks.
But, by all means, people should work on stuff they love. There's no way a small, bootstrapped, startup can possibly weather the hardships in the beginning, when money is tight, rewards are few, and everything takes longer than expected, without having a real passion for the work they're doing.