That's a really good question, sir.
Right now, public blockchains such as Bitcoin and Ethereum have all had scalability issues. They're the most secure blockchains out there right now, because they've been tested over years, but they do have scalability issues. Some of the enterprise blockchains, the permission blockchains such as Hyperledger and Corda, and other platforms, are actively working on the scalability issue. For example, I run a start-up and we build on Corda, and we're trying to build a platform that can do millions of transactions every second, because we're building a trading platform.
This is one of the biggest problems being worked on in the blockchain world. I don't believe anyone has a solid result yet, but the blockchain world is so young that I would say in the next six to 18 to 24 months we're going to have some very scalable solutions. That being said, I don't ever see a blockchain art registry having as many transactions as, say, a stock exchange on blockchain. They're building platforms for stock exchanges, so that technology could very well be used for an art registry.
Although it is a problem today, it is not something I believe will be a huge sticking point in the future.