What is missing from the picture
A domain name involves a registry, a registrar, name servers and usually a certificate authority. Every one of those is an organisation that can be contacted, ordered, hacked or bought, and every one of them can change where a name points. That is not a flaw in the design. It is the design, because domains were built to be administered.
An onion address has none of them. There is no organisation holding a record of who owns it, because there is no record of ownership at all. The address is a public key. Whoever holds the matching private key can answer on it, and whoever does not, cannot. There is no third party in the position to change that, which means there is no third party who can be persuaded to.
What that actually protects
- No registrar can transfer the address to somebody else, because no registrar has it.
- No name server can be poisoned into pointing it elsewhere, because no lookup of that kind happens.
- No certificate authority can issue credentials for it to the wrong party, because none is involved.
- It cannot expire, because there is nothing to renew and nobody to renew it with.
- It cannot be seized as a name, because a name is not what it is.
What it leaves completely open
The entire class of attacks that remains is the one that works on you rather than on the infrastructure. Nobody needs to take an address away from its holder if they can simply give you a different address and have you accept it. The cryptography is not involved in that transaction at all, because it never gets a chance to be.
This is why publication is the weak point and always has been. The strings themselves are unforgeable. The claim that a particular string belongs to a particular service is a completely ordinary claim made by ordinary means, and it can be wrong or dishonest exactly like any other claim on the internet.
It is also why this site is careful about what it says. It can compute properties of twelve strings and it does. It cannot establish that those twelve strings are the ones the market published, because that is a question about publication and not about characters. What a published set is goes into where that leaves a reader.
Questions
Can law enforcement seize an onion address?
Not the address as a name, because there is no registry holding it. What can be seized is the machine holding the private key, which is a different action with a different effect.
Can a TorZon address expire and be registered by someone else?
No. There is no registration and no expiry. If the key is never used again the address simply stops answering, and nobody else can take it up.