The whole problem is in the way people who want continuations of Tolkien's stories are looking at this. Its as if they see Middle-earth as equivalent to Ancient Egypt . A Historian writes a series of books on the history of Egypt, but leaves gaps in the narrative. Unfortunately he dies before he can complete his project, but some readers are so fascinated by the period that they demand other historians take up the baton & complete the story. And that's possible because Egypt has a history, & the truth about it can be discovered & made available.
Now, Middle-earth in not like that. The gaps in the story are there because Tolkien never invented anything to fill them. There is nothing to be discovered. The fact that Tolkien failed to fill the gaps, while at the same time focussing on other parts of the story to the extent that he re-wrote them over & over, tells us a great deal about the man who invented the world. To 'fill' those gaps is effectively to create a false impression of the creation.
Look. its like an American fan wishing that Tolkien had visited the US in the 50's to promote LotR. The fan decides that in order to satisfy his desire he will invent a promotional tour by Tolkien, including meetings with prominent American fantasy & Science Fiction writers, & attempt to get this included in a reprint of Carpenter's biography - why not, if its a good story, well written, & serves to entertain other Tolkien fans?
Well, because its not true. Tolkien never went to America in the 50's. Just as Tolkien never completed his Legendarium. But its incompleteness is part of its nature. To add new stories by new writers just to 'fill in the gaps' is equivalent to deciding to stick arms on the Venus de Milo. Of course you could get a decent sculptor to knock up a pair of arms & attach them in order to 'finish the thing off' - in fact, that at least could be justified in that the statue did have arms at one time.
But look at this, an unfinished work by Michelangelo
http://www.ablemuse.com/premiere/bho...unfinished.htm
Should we hire someone competent to finish it off? Read the accompanying poem. If we got someone to finish off the sculpture, what, exactly would we have gained, in comparison to what we would lose?
Its the very fact that the Legendarium is incomplete that adds to the poignancy, the feeling of what might have been, if only...
Its a metaphor for life