Our source also provided us with a couple of User Agent profiles. One reveals the model numbers of some LG Optimus G Pro models that are being tested with Android 4.4. The other shows model numbers and the supporting carrier for some LG Optimus G units being tested for Android 4.4.
You might recall the outpouring of emotions that took place when a poorly worded Facebook entry from LG's Estonia division made it appear as though the LG Optimus G was receiving the Android 4.4 update there, in advance of both the LG G2 and the LG Optimus G Pro. As it turned out, the phone was merely getting an update that would allow it to support 4G. If LG thinks the testing is favorable, the handset could be loaded with Android 4.4 for real.
Thanks, Anonymous Tipster!