A few non-editorial related comments:
- I raised a similar idea for an on-chain key registry in Pretty good privacy (PGP / GPG) on-chain keyserver. Happy to see someone else exploring the same space!
- Using an enumeration for key types might limit the future expandability of the standard. What if a new algorithm comes along?
- It might be a good idea to allow users to store one public key per algorithm, instead of just one per user, and further, you might want to allow users to store separate signing/encryption keys for validation vs. encryption.