Seemingly because not all Windows Phone 8 users have received the GDR2 update yet, Microsoft and Google have come to an agreement that will provide air cover for Windows Phone users setting up new Google calendar and contact synchronization.
Update: A couple of readers who have GDR2 have noted that CalDAV/CardDAV support is, indeed, part of the update. Here's some proof.
Update 2: Microsoft also confirmed GDR2 does include CalDAV/CardDAV, even though the Windows Phone Update site doesn't mention these features. A spokesperson provided me with the same statement Microsoft is giving others about the extension of the cut-off deadline with Google: "We’ve reached an agreement with Google to extend support for new Windows Phone connections to the Google Sync service through December 31, 2013."
Update 3: The key word here, it's worth noting is "new." This date extension is relevant only for new Windows Phone connections to Google Sync. For Windows Phone users with existing Google Sync connections, it's business as usual. Windows Phone users who already have Google Synhc connections are able to connect to Google calendar and contacts even without the Google CalDAV and CardDAV support in GDR2, and will continue to be able to do so after December 31, 2013. The just-announced extension is for Windows Phone users who've bought new phones and are looking to sign into Google Sync for the first time.
The next Windows Phone 8 OS update is GDR 3. GDR3 allegedly is targeted to arrive this fall. This OS update allegedly will add support for five- to six-inch devices with 1080p support. Along with the higher resolution, GDR3 also could include changes in the start screen and core Windows Phone 8 apps, such as possibly adding a third column of mid-size-tiled apps in the start screen.
The Microsoft-Google dance over CalDAV and CardDAV support has been a complicated one.
At the end of January 2013, Microsoft and Google came to a last-minute agreement to extend Google's support of Google Sync, which is built on Microsoft's Exchange ActiveSync, until July 31 -- instead of terminating it by the end of January, 2013, as previously announced. In the interim, Microsoft would build support into the Windows Phone operating system for CalDAV and CardDAV, the Google calendar and contacts sync protocols, the companies announced.
But then in March, Google announced CalDAV API support was being discontinued on September 16, 2013, with the Google Calendar API becoming the CalDAV replacement. However, according to Google's blog post on the topic, some unnamed "whitelisted" developers would be able to continue to use CalDAV. Microsoft is one of those on the white list.