This discovery was by accident. shanmukha24, the aforementioned XDA forum member, sent in his LG Optimus G Pro for service. After his smartphone was returned to him, he discovered that it was now running Android 4.4.2 already. The person who worked on the device then revealed that an official update would be making its way out to device very soon, probably in a month.
It is not surprising to hear of some older devices receiving Android 4.4, though this is probably the first time that the Optimus G Pro was ever mentioned even in passing. With all the focus LG is showering on its successor, the LG G Pro 2, this news will most likely make owners of this early 2013 flagship quite happy.
Of course, nothing is official yet, but even though there's still a chance it might not happen at all, there is still a sliver of hope. There is currently an attempt to extract the Android 4.4 image from the device so that it can later be shared with other owners, as a backup in case LG decides not to push through with the update.