Ok, I will go in order here
What does it take to make it on the leaderboards? Do I need to stream or have video evidence?
You have to stream almost your entire playthrough, to get on the leaderboards it looks like you have to clear at least one or two bosses in the devas
Will the game be continued after Plynq made that video? (I don't blame Plynq, Kamilia just needs to learn that not everything can go his way
It might be continued, he cancelled time and time again and he never meant it, besides, Plynq's video was his choice, and it was about revenge, he is mostly responsible (No offence intended)
What is the hardest room/boss in the game for most people (not boss rush)?
You're not being specific with this question at all, and it's a matter of opinion, for most people right now, the hardest part is Secret 5, and as for bosses without devas, maybe Cyber or Gravity Man.
What is the latest version? If that version is private then what is the latest public version?
Version 1.25 and it's public
https://www.mediafire.com/download/n6sbawc3qo20rtj/I+Wanna+Kill+The+Kamilia+3+v1.25.zip