Afterwards, the idea for Sailor Moon Crystal is from Naoko Takeuchi.
Although I love the 90 anime, you have to be realistic, the end closes the story. I don't see how they could come up with a new story that holds up. Since the confrontation against Galaxia / Chaos is the outcome.
Doing a sequel to the manga but instead of it being in print, but in an anime version, can be doable.
There is material in the story. The Neo Queen Serenity's era, Sailor Cosmos, Sailor Chaos, there really is plenty to do.