OK, I have a good news for K4 users. Following geekmaster and hawhill's instructions, I successfully ported KPV's eink control module to K4. Following is a screen cast of my friend's K4 running the next generation of KPV with the new UI framework. It is displaying a test PDF document.
Now we need to finish the UI framework ASAP and write lots of menus, because we only 9 keys on K4 ;P