Not really...crypto is the biggest one that people cite, but the crypto ecosystem seems to be humming along. It hasn't taken over the world, but it also hasn't really fizzled imo. I haven't really paid attention to whether VCs are still investing there.

I guess maybe VR is another one? But that's another example of a slowly growing ecosystem.

I think mostly the people who think some piece of hot tech is going to take over the world aren't usually wrong, they're just early.