I don't know where to find the quote now, but I'm pretty sure he had said he wanted in time other writers and artists to add to his mythology. He knew full well no great mythology is formed entirely from the mind of only one person. And I include in that both adding to the continuity and creating alternate continuities.
As massive as what he left us is, there is also much room to expand, even without continuing the story past the reign of Aragorn's son. And if you do go past that the options are endless.
I think he would have wanted people with different backgrounds and experiences and perspectives then him to explore Arda in ways he couldn't. So yes I think that includes women writers adding a female perspective. Both further developing the female characters he already provided and creating more of them. That is part of my defense of how lacking his handling of women was.
I think there is room even to expand Arda beyond just Middle-Earth, Numenor and Beleriand, and explore other less western (white) civilizations. The Southorns and Easterlings get a bad wrap as seemingly just pawns of Morgoth and Sauron. But Tolkien did leave more then enough hints that their being in that situation is not really their fault. I love Faramir's speech at the end of disc one of The Two Towers extended edition. In the book Sam said it, but I think that's one of the things the movies improved, Tolkien had described Faramir as the most like himself, and I see those words as coming from Tolkien's experience as a WWI solider.
I think it's also plausible to create all new Civilizations for Arda. Both outside Middle Earth and maybe even within it. During the second age we know next to nothing about the humans who lived in Middle Earth rather then Numenor. Then there is the fact that the lands of Middle Earth did exist during the First Age, but the story of the First Age is entirely further west. Why not invent some matriarchal Amazon like tribes for Arda, both within Middle Earth and without. Some Edain Amazons who could make sense coming from an offshoot of Haleth's tribe, and some others too.
And the Dwarves (who had 7 clans but we only really ever see one) are equally as open. The Dwarves seem far less likely to have ever had a matriarchal tribe, but the feminine side of the Dwarves is still entirely open for new writers.
Now it may seem difficult to believe a devout prudish Catholic like Tolkien would ever be Ok with Homosexuality being explored in his mythology. But he also talked about Applicability, that a story should be interpreted beyond the Author's intent, even in conflict with it.
And you know what, I think it's telling that Tolkien never condemned Homosexuality at any point in his Legendarium (Lewis did with the Hardcaslte character in The Hideous Strength). In-spite of how G rated his writing was when it came to Sex, he did address sex acts he viewed as wrong. Eol and Ar-Pharazon are both Rapists in at least one version of their tales.
And Incest is explored, most famously with The Children of Hurin. But what most annoys me about Tolkien's sexual morality is how harsh he is even to relationships between First Cousins. The Bible not only never condemns it but even encourages it to an extent. For the most part being grossed out by Cousin relationships is entirely modern, or Victorian in origin perhaps. But Tolkien not only codifies it as wrong in Elvish law, but has it at the root of Meaglin becoming the Elvish Benedict Arnold.
So that he considered Same-Sex love less worth condemning then Cousin love, is interesting. Tolkien also enjoyed a Lesbian Nurse Story.
Everyone has talked endlessly about the things in Tolkien that can be interpreted as male Homoerotisism. But since Tolkien never passes the Bechel Test, actual relationships between women are virtually non existent. So we have to look elsewhere for an excuse to interpret a character as Lesbian.
Tolkien may not have been aware of it, but it is now well known that Virginity in the ancient mythologies Tolkien drew on was often code for Lesbianism. The most popular Tolkien character to see as possibly Lesbian by virtue of her seeming aversion to men is Tar-Ancalmine. Unfortunately she seems to make a very problematic stereotype whatever orientation you give her.
The top two women in Tolkien I like to interpret as Monosexually Lesbian are Haleth and Tar-Telperien. Both were leaders of their people who made a point of never being married.
Haleth as an early First Age human I don't even visualize as a Medieval person. The Human tribes during the First Age I see as Ancient, but not Greeco-Roman Ancient, more like the Ancient pre-civilized Celtic and German/Norse tribes. Haleth however seems to me like exactly the kind of woman who would wind up being a lover of Artemis. Since I see some of Artemis in Nessa, I wind up shipping them together. But there is also room to invent for her a human lover from her tribe, or have her meet an Elf. A human from another tribe seems unlikely as I think she was always pretty far away from them.
Tar-Telperien, I have seen two people in the Fandom community already say she is Asexual in their head canon. That is an equally valid interpretation from what little we are told about her. But I really want to see a High Fantasy story about a Lesbian Queen, with a lover probably from a lower class. Possibly drawing some inspiration from Berenice and Mesopotamia (free cookie if you know what I'm referencing). And as far as room for that in Tolkien goes, Tar-Telperien is the best option.
All three Queens of Numenor get a bad wrap. I feel like Tar-Telperien is the easiest to defend. Her condemnation is entirely in her foreign policy. Crap was going on in Middle Earth between Sauron and The Elves, and she choose to stay out of it. In real life that is exactly the foreign policy I prefer as a former Ron Paul voter, The U.S. should stay out of wars fought on other Continents. It's hard to apply that to a fantasy setting where one of the Geo-Political entities is a literal Fallen Angel. And I'm sure Tolkien had the WWII era American Isolationists in mind when he wrote characters like this. But I for one will not condemn her for refusing to take her people to a war that did not really involve them.
She is also notable for being the only Ruling Queen who's known to have had a brother. Speculation on that has been done elsewhere. What I note here is the fact that her brother's son became her successor, and we do not know a name or identity for the mother of that son. I think it's possible that if Tar-Telperien was exclusively Homosexual, but had a lover who was Bi/Pansexual, or at least more open to male-female intercourse for the purpose of reproduction then she was. I could see her marrying her lover to her brother.
I do indeed consider the possibly of actual legal Gay Marriage in Arda unlikely, For the Elves Hetero-Intercourse and Marriage are the same thing. We've seen in Fantasy and maybe History also examples of something like the above suggested arrangement with men. A man in a royal gay male paring marrying his lover's sister. Like Renly and Loras on Game of Thrones.
The Tolkien women who have loved men could certainly still be Bi. But there is one more character I want to discus who's Sexuality is entirely up for debate.
Nienor Niniel, daughter of Hurin and sister of Turn Turambar. Her relationship with her brother came about from the dragon Glaurung's manipulation of events, an argument can be made it tells us nothing about her actual Sexual Orientation.
You may be thinking "all he did it seems was wipe her memory?". The key thing I think in Tolkien's mind was that their ignorance of their relationship to each other caused their natural sibling bond to be misinterpreted as romantic. It didn't at all happen simply because she thought Turambar was Hot.
I found one Fan Fiction once were Niniel had a romantic relationship with Nellas before she went to search for Turin. Then she survives her jump into the water, Nellas tracks her down and they raise the baby together.