I'm not that happy that the lock has to communicate with a central server. For one, that adds all sorts of dependencies (the internet, central service, etc. have to be up for the unlock command to work). For another, what if there is a security compromise of the central server?

I'd much rather have a system where the lock uses an NFC sensor and a CPU, and it works with phones that have NFC. Yes, you wouldn't be able to do remote revocation (you'd have to be standing in front of the lock to send an updated CRL), but it would be a lot more secure, and it avoids dependence on a central server.