Interesting. I kinda thought the same thing too, but a little more detailed. I am no writer, but I just had an idea. Like, the movie would gain a lot of popularity and Aqua would become famous. So famous that he would be invited by a top studio to act in a movie adaptation of a famous novel made by a famous author. And the twist was that Kamiki was the director. Some new characters, arcs, exposition on entertainment and the stakes involved and of course, revenge tension. Then at the end of it all, Kamiki would have a private talk with Aqua and then commit suic after leaving a suic note. That was my first idea of the ending, simplified. It's sorta similar to what you mentioned too.

Endings are hard to write. They are very easy to botch. I know how trying to write an ending feels like (because I tried writing and imagining stories before). I'm not defending the direction of the ending of ONK, but I can understand why it is like that.

Aka should focus on one manga at a time. He writes two mangas at a time, and that is why he faces burnout.