While I get the sentiment, I think things relating to the Outer Planes should have some ambiguity to them. Otherwise outer planes just become nice locales with different colour palettes, and you don't get anything majorly religion-y or mysterious about them. So for me the problem in your example wouldn't be the Khajit having an objectively wrong view, but the games giving you an objectively right experience of things that should be left open-ended.
I'm with the people talking about just putting crystal spheres back in. The whole "coexisting" on two planes at once and talking about superpositions is too much. I'm using crystal spheres. Once you leave the sphere you travel to the Astral Sea. Done. So much simpler than whatever "slow entry into the Astral Plane" thing they're using now.
I'm sticking with the idea I posted upthread, where you pass through a portal to the Astral if you approach the edge of the Wildspace system at spelljamming speeds, but if you don't you come against the crystal sphere, from which you can pass through into the Phlogiston. The Flow is actually faster travel than the Astral, but it has all the flammability issues of the old Phlogiston, it's pretty empty, and what is out there is Great Old One level dangerous. Thus, most people use the Astral.
I'm glad to see that none of the Spelljammer UA races got cut. And I'm hella interested in seeing HOW the Thri-Keen's arms and the Plasmoids' abilities turned out/changed.
*On the flip side, no matter what, you can use the rules for the Thri-Keen's four arms for kitbashing/customizing for any races that have four arms, like a Marilith race for pcs. (Which is already taking the Kobold Press midgard Lamia pc race and attaching the 5E Thri-Kreen arms on it. And then go from there.)
That was my plan too. The Astral Sea will be both hyperspace and an undersea equivalent. Maybe I'll even give some bad guys an experimental Spelljammer Helm that lets them emerge anywhere inside of Wildspace, to essentially give them a "submarine".