I’ve long ascribed to (and felt) that people are existentially isolated
There’s a pair of conjoined craniopagus twins in Canada, the Hogan twins, who are conjoined at the head and have fused brains connected by a thalamic bridge. They’re separate individuals who still receive some sensory awareness of what the other is feeling, and they can even communicate in their thoughts. When one was crying as a child, you could put a pacifier in the other’s mouth and they would both calm down. When you cover one’s eyes and show an image to the other, the blindfolded one can see it.
To the best of my knowledge, neither one of them has ever once said that anything was particularly different about how the other sensed something. Tatiana’s red is still Krista’s red, and so on.
The claim of existential isolation is a bit like claims from centuries ago about how it fundamentally couldn’t be known whether a person blind from birth, if given the gift of sight, would be able to look at things they’ve only touched up until then and identify them. If you think of a clever enough situation, or if a sufficiently serendipitous medical oddity arises, seemingly intractable problems of that sort can be defeated rather anticlimactically.
Did you ever end up making a Part 2?