It's an oldie theme, but ever since rgveda started pushing his post-stars work, I felt it was just the wrong direction to keep endlessly escalating on one end, and rehashing on the other. Expansion should go sideways, and power stay consistent (unlike say a wow expansion pack's creep) and branches should go off exploring paths unseen.
with that I present my recently discarded post-stars idea.
The premise is, that at the culmination of Sailor Cosmos ans Sailor Chaos battling, the galaxy cauldron is destroyed, and the power held within is released to permeate all of existence. Worlds, civilizations are wiped, and the "new people" slowly begin to rebuild unaware of the past.
Sailor Cosmos, and those senshi who havent died yet, are now little more than disembodied ghosts wandering the vastness of space, relics of a forgotten age.
As for the new people, they live in a world permeated with the magic once only the chosen few could wield. This time, anyone could pick up the knowledge (and practce) to harness some of that power. This energy is a mixture of cosmos and chaos, and so there aren't any strict lines like "Oh, the sisters and sapphire are finally on the side of good. too bad they cant use their once magnificent power to help out" dung pie.
So for the story, it'd have been about a young girl from a rural town, and a young, but more mature millitia recruit setting out to seek out a recently fallen star (comet) near their town. There they find the ghost of Sailor Mars wander around, who only the girl can see, but both can hear.
Sailor Mars would explain to them that while she is a spirit, wandering the cosmos, trying to reunite with Sailor Moon, a dark presence has chained her to the planet, and she was looking for the comet to provide her with some clue, help, or anything.
They take pity on her, and resolve to get to the bottom of this. Along the journey, they'd run from monsters in a swamp, traverse rocky and stormy coastlines reminiscent of england's, grow in strength and skill (for the fighter), or magic (for the girl), and find the culprit being based in the ruins of an old city, from the time of chaos and cosmos.