Shipment tracking, Stocks delivery and settlement, the government official gazette. These are three I'm thinking of. Sure, you can do it with a centralized server, but a decentralized alternative can offer some kind of "Open World API".

Now for a true defi, you can't depend on the physical world (some authority out-there). Only cryptocurrencies are possible in this case, and maybe, if the blockchain becomes advanced enough: Dynamic value derivatives denominated in crypto.

It might sound as limited but money (and the transfer of it) is kinda a huge thing. Crypto's downside is volatility. Being able to hold crypto as crypto while preserving stability (or better: value) will be a game changer. It'll also mean KYC and regulation will be harder to implement.

KYC/regulation/blacklisting are huge tools for governments. Government can have control over centralized entities (ie: an exchange, a bank, etc...) but they can't control everyone's wallet. They might be able to mess with a couple guys or figure out if a certain gang used such and such, but it'll be impossible to track everyone transactions that are happening in the blockchain (worse, the "whole world" is out there). And even worse: Current events have showed that governments are way behind when it comes to blockchain technologies. Some governments are not even aware of its existence or meaning.

In my opinion, this is huge. Most societies/civilizations collapsed when they failed to collect taxes. Peasants (your lovely citizens) are unlikely to pay when given the opportunity. Less taxes means less control, it's a slippery slope. Bad news for many governments around the world.