If they want to do ships in the Astral and use them to travel from location to location, that's cool with me.
But Spelljammer takes place in space. There aren't any of the space hazards in the Astral: it's timeless, so you don't need to breathe, eat, or drink, and maintaining your 'jammer's air envelope and making you have enough provisions on your ship is actually important in Spelljammer. The lack of gravity doesn't even work in the same way: Spelljammer at least pretends to use physics in the way freefall works, meaning falling overboard is actually risky. In the Astral, you can just think yourself wherever you want to go. And unless they completely rewrite the Astral, there's also no planets, asteroids, comets, or--as TV Tropes puts it--negative space wedgies there, while they exist in spades in Spelljammer. Nor would most of the kooky space opera/Star Trek/misc. space anime creatures or events of Spelljammer really fit into the Astral.
Yes, it's possible for them to do the Astral Sea, but I really don't think that they'll be able to do Spelljammer that way. They're just too different.