I liked how, in your review, you compared SubaHibi to that of an unsolved equation with a large amount of parts that comprised its whole. That is very true, and SubaHibi is indeed mainly recognized by a lot of people as a story which can only be freely interpreted in a subjective manner by the audience, since only Sca-ji really possesses the answer to the equation. However, from my own experience, I can't say I completely agree with that (which I'll explain why at the end of my post).
Of course, to what extent you look into this story depends on how much of an utter completionist/perfectionist you are. In theory, understanding what SubaHibi's plot 'is' would make it all the more clear what the meaning, the message, the thematic significance of the story is. With my current perception of the story, I wouldn't be able to bounce off my ideas on those things to others without first going into my idea of the equation's answer (especially if it's concerning Zakuro and Rabbit-Hole I).
Here are my answers to you on those points you bring up as "A" and "B" (I can't fit the other points about Zakuro and the Gondola Ride here, so...):
which is by default given to people when born.")
I really hope that I was able to present this in the least convoluted way possible. Though I would still recommend you take a second or perhaps third look at everything. (Especially
I think that SubaHibi's story, as an 'unsolved equation', most certainly has its sole answer embedded somewhere within the story. It's just in such a place that no one would ever think to look.