The phrase "to be continued" is a kind of set phrase we often see at the end of part of a story, a television show etc., and I believe it is an abbreviation for "The story (or the show etc.) is to be continued." In this case, I can think of some other variations of this sentence like the following:

1. The story is *to continue*.
2. The story *is going to continue*.
3. The story *is going to be continued*.
4. The story *will continue*.
5. The story *will be continued*.

If the five sentences are all correct, then is there any difference in meaning or implied nuance between "to be continued" and the other alternatives above? I wonder what makes the phrase "to be continued." so idiomatic?