Notes is now using CloudKit to synchronize between OS X and iOS
iCloud Backup is now using CloudKit
Apple can offer developers a huge amount of storage. I'd say watch the session video, my notes would just consist of repetitions of "Huge amount of storage, costs you nothing."
CloudKit Web Services
Full CloudKit API vs JSON / HTTPS
Sign-in via Apple ID
Web sign-in with Apple ID
Retrieving data ...