I have to declare an interest here. Unless we are talking about a series where the next one is available right now, I’m not really interested in open ended stories. I suspect they are lazy. If I wanted to make up my own story, I wouldn’t be bothering to read yours.
But there are many people who enjoy this stimulation to the imagination. If you want to please those people, try this post about how to write a story with a great open ending.
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