@d15to here's how I see it being possible (not even remotely likely, mind you, but possible)
We've had numerous hints that Tsukasa is extremely long lived and has something to do with the moon/space.
What if she's an alien?
What if she is not only an alien but from the same species that will eventually conquer earth in ad astra?
What if not only that, but she is also a member of the imperial family? Who, disapproving of her family's/species' conquering ways, is hiding out on earth?
She marries Nasa, has kids, grandkids, great grandkids, and so on, until eventually...
the protagonist of ad astra is born. (I forget his name. it's been a while since i've read it, so I'm fuzzy on a lot of the details.)
What if part of the rationale behind him being able to pilot versailles is because he's descended from a member of the imperial family?
Then all you have to do is throw in some time travel (and there have been far more ridiculous plot elements in Hata's manga so why not?) and there you go: crossover.
Until the plot progresses enough that this becomes impossible this is what I'm going with.