The reason why I want this to be the last, and I have gotten this question from a lot of people, is because I want to try writing different stories. The Revenge stories have followed the same format the last two stories to the point where if I were to write a fourth story, it would get stale. I've tried to vary how the stories worked every single time, and I'm finding it harder and harder each time. I don't want to repeat anything from previous stories, so I have to make each story unique in its own way. So I feel that if I were to write a fourth story, I would lose my own interest in it, and I feel that others would too.
Having said that, I do like the idea that you came up with. Unfortunately, after Revenge III I will either write a different story that I already have plans for or just take a break from writing in general.
Thank you though for your thoughts.