Saurik has "flipped the switch" in Cydia to allow purchases for device and OS-compatible jailbreak apps and tweaks for iOS 9. That means that any tweak that has been properly updated for iOS 9 can now be enabled for sale by Cydia developers.
While this is a definite first step to being able to have a normal Cydia experience with the iOS 9 jailbreak, developers will still have to update packages and enable their tweaks and apps for sale. In other words, you may find a handful of tweaks out there that can be properly purchased and downloaded, but it's still going to take a while for developers to properly catch up.