For anything physical you will always need the legal system as a backup. That said, you could imagine using smart locks that are connected to the blockchain an

For anything physical you will always need the legal system as a backup. That said, you could imagine using smart locks that are connected to the blockchain and using smartcards for keys. Then at least key management is "solved". I put it in quotes because again, it's the physical world so there's still the issue that the smart lock could be broken and blockchain can't do anything about it. I don't think it makes sense for rentals because that field is heavily regulated and in a lot of jurisdictions you can't just lock out tenants when they're a day late on payment. It could make sense for something like standardizing gym access. For 24 hour gyms there's already systems to get access when no staff is present. You could imagine a blockchain based solution to manage that in a standardized way that could work across different gym chains. The advantage would be that pay-per-use is handled in an automatic way, gyms that want to join the network just need some hardware for access and they're good to go. As a user you wouldn't have to sign up for a different gym every time you move. The big issue is that most gyms don't want pay per use, they want to sell subscriptions knowing that most people end up not going after a few times. The above solution could also obviously be implemented by a centralized provider without using blockchain. Blockchain would be a marketing angle I guess and might help convince investors to give you money.