LG G Flex (SK, KT & LG U+) can be updated to 4.4.2 from now onward....
Update link (in Korean): LG Mobile : 다운로드센터
From source: LG G Flex, Optimus G Pro and VU 3 Receiving Android 4.4 KitKat Update
my wife got kit kat on her G2 on T mobile almost 2 weeks ago; I assume the flex will be really soon as well..