Explanation of what subjects we can use in subject-verb inversion:
From an answer to “Here he comes”, “Here comes he” : The order of pronoun and verb in inversion:
1. On the corner is a cafe. – correct because “a cafe” is new information (due to using “a”) and, therefore, can be transported to the end of the sentence where it receives the most emphasis
2. Here comes he. – odd (not idiomatic) because “he” is in a very prominent position at the end of the sentence. This position would normally be reserved for new entities. But the fact that we are using a pronoun here means that we must already have been talking about this man in the previous discourse.
Examples which contradict the explanation:
3. Out of the tree fell the squirrel.
4. After the speeches came the toasts.
From a textbook:
5. The door opened and in came the doctor.
6. As soon as I let go of the string, up went the balloon, high into the sky.
Following the explanation above:
The fact that we are using "the" with "squirrel", "toasts", "doctor" and "balloon" means that we must already have been talking about these subjects in the previous discourse. Hence we can't place them in a very prominent position at the end of the sentences, as in 3.-6.
But since 3.-6. are correct, then is the explanation given at the beginning of the post wrong?