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I was thinking "invert" the ND to hold back the foreground illumination, while you gather all the light you can for the stars.
It could "stand alone" as a single exposure (not sure @ ND value desired), or ... if you wanted ... then, it would be an easy matter to shoot a second image without the ND (or flipped), exposing for the foreground (generating black sky) and you could blend the two to taste.
Just gotta find a time/technique where those pesky clouds don't steal from the astro show ... balancing act that might be best approached at one vs. the other, challenging either way.
Ok, gotcha, that may work, never thought of reversing the nd grad. Your idea made me consider another. I could do one shot while the moon was up and another after it sat. Then blend the results.
I once did this only reverse, I took a shot just at sunset for the foreground then waited for total dark while freezing half to death. But it turns out I was pointing wrong for the milky way. I was still able to blend, but it looks pretty fake.
Here is what it looked like, the milky way is 4 shots stacked, the foreground is pasted from an earlier shot.