On Thursday, the Cydia founder himself, Saurik, announced over Twitter that purchases in Cydia are now enabled once again. Since the iOS 8 Jailbreak was released, purchases were made inert due to stability issue, which seem to have been fixed now.
This is great for Cydia vendors as well since developers can now mark their products as iOS 8 compatible. The next few weeks should be exciting as Jailbreak developers begin to update tweaks and themes for iOS 8.