Google should release betas for major Android updates like Apple, so devs can update their apps
Since there are now Nexus devices and Google Edition phones, Google could easily release betas for these flagship devices before a wide-spread release. You can bet that iOS developers will quickly update their apps during this iOS7 beta period to take advantage of the new UI and APIs. By the time the official release comes around there will be very little apps with the old UI.
In contrast, there are still popular apps on the Play Store with Gingerbread elements or Holo with half-assed execution. Granted, it's been nearly 2 years since the new design guidelines were introduced and they should have updated their apps by now. However, if a beta period was specifically set aside for them, maybe it would spur them to adopt the new guidelines and make sure their apps are stable.
You can almost guarantee that with KLP, a Card UI will be system-wide and the design guidelines would be updated again. If time was set aside for developers to adopt this, there would be a whole consistency to apps in the Play Store.