But it is possible right, I mean there is no limitations in the hardware that makes the KXXX series unable to handle flash themes, so it should somehow be possible to customize a firmware to enable the flash support for the K8XX series?

-->SMD
I think the ones you are referring to is possibly some who has flashed to K770 firmware, since it supports flash menu, I tried it myself, but you looses the ability to use the joystick, and no camera or radio, so it is pretty useless in the long run IMO.