Of coures useless to those using 1Password with Windows and Android.
What comes first, security for users, or marketing a new release?
If this new format is more secure and ready to roll out, why delay?
What if Mavericks doesn't get released in October but gets pushed back to sometime next year?
The Cloud Keychain format is currently used in 1Password 4 for iOS.
1Password 4 for Mac is also in public beta and will probably be released around the same time as OS X Mavericks.