I think the real irony is that AirBnB is their biggest darling, and it's not a tech company. The history of that company is very interesting, going back to Paul Graham making a note of them being the first founders without a technical background to get into YC (the third cofounder who is technical was added to the roster later on, or at least given the title).
That said, I have high hopes for Stripe, Ginkgo Bioworks, Gusto, Docker, Gitlab, and some of their other companies (not that they'll necessarily go public, but that they'll become real companies - I'd argue this describes twitch).
Maybe I'm being too optimistic with Gitlab. I know next to nothing about their business, other than hearing good things from people who have used it.
That said, I doubt I would've seriously considered investing in any of them except for Stripe until the previously listed companies had shown significant traction. I'm actually somewhat pessimistic about AirBnB's valuation 5-10 years from now compared to today.
But then, I thought for sure the iPhone was going to flop. So what do I know?
Docker is just as much in danger of being clobbered by the cloud providers as ElasticCo, Mongo and all of the other open source companies. AWS is making money off of us running Docker. Docker itself is not making any money from us.
But the number of tech startups that go public is small. Only one YC backed company has ever gone public - Dropbox. And it seems to be proving Steve Jobs right. It was never a product, it was a feature. It still doesn’t have a clear road to sustainable profitability.
Even out of the few that have gone public within the last 10 years, most of the tech darlings still haven’t become profitable.