Well, we already have more than enough ways to pay for stuff digitally and most of them are already very easy to use, very fast and secure enough. Therefore I think it's relatively safe to say that blockchains, at least for payments, is not the next big thing.

If you work in the field, you could simply look out for things that are expensive, slow, hard, or all three and if someone is trying to fix thay.

One thing that comes into my mind are private cloud services. There aren't any good locally installable cloud platforms. There seems to be a rising need for private clouds and/or "user verifiable cloud services" aka. more or less "locally installable AWS" or a way to be sure that when you buy some cloud service, there is no way your data can leak anywhere at any point.

Speaking of verifications, guarantees and such, one interesting concept I've been looking into lately are zero knowledge proofs. Simply put, they would be a way for person A to prove to person B something about X, without revealing anything (sensitive) about X.