But as noted in the article, that's not the case. OpenSea stores data that then isn't on any blockchain, like royalties. That's done as just a regular web2 feature, a database on OpenSea's backend.
So no, it can't be validated, and it can't be migrated.
Royalties is a funny example because a) they’re being standardized, see eips.ethereum.org/EIPS/eip-2981 and b) royalties are entirely opt-in. You can happily transfer NFTs without having to pay royalties if you forgo an exchange that respects them.
That’s literally one of the most salient points of TFA: protocols move dog slow and provide too little too late, platforms iterate fast and give people what they want right now.
But there will be other features over time, that would not be standardized. As per article centralized platforms progress faster than decentralized standardization. Switching cost will grow.
So no, it can't be validated, and it can't be migrated.