Christopher Tolkien did mention those “writings”, in fact the last three published books by him (Sons of hurin, Beren and Luthien, and The fall of Gondolin) are based on those, if I’m not wrong.
But those three stories are not new, and they are just expansions, other points of view or corrections around the facts explained on The Silmarilion and the Unfinished tales.
It seems strange to me that, on his (C.Tolkien) super-detailed studies and commentaries on those three books, he did not mention anywhere this “new stories” not sure if I have to be afraid of that book or be happy with it…
But most of you have more expertise on this than myself, so I hope some of you might tell me if I am to be happy with this new announcement or not.
ON the other hand and unrelated to this, I am also afraid that the lotron prime series became full of sex/nudity/blood/raw language and other things that I do not want on high fantasy Tolkien stories. (Although I appreciate it on other series, such as Vikings or Game of Thrones)