The CI is not a thought experiment. It describes an aspect of reality. I am absolutely not equiped to explain Kant, but if I had to I would use quantum physics to make things easier.

Imagine Schrödinger's cat. This is no metaphor, we can build such a construction. (the real star of that show would not be the cat, but the total causal isolation we need to place her in) According to almost two centuries of quantum research, much to the chagrin of Einstein, God does play dice. There is spooky action at a distance. We do not measure reality; instead reality is created wherever we measure.

The way I understand Kant, he had a deep understanding before it was cool.

This is why he objected to Leibniz and Newton's "pure reasoning", as indeed (regarding your other question today) many other continentals like Decartes were trying.

His CI cannot be split from this view of reality. I think what Kant tries to convey here, is that morality is more real than reality. And that certain aspects of morality are truer than empirical fact itself.

P.S. My personal conceptual understanding of Kant may differ from yours, as this is hardcore metaphysics, which by its nature is experiential and perhaps spiritual, in the dryest sense of the word.