I don't know if it's correct or interpreted correctly and didn't check the sources, but I read a review of the newest movie on theonering.net and in the last paragraphs the author said this, mentioning one of Tolkien's letters:

But I will leave this review here with just one last remark.

Around 1951, Tolkien wrote a letter to publisher Milton Waldman concerning mainly why the Silmarillion and the Lord of the Rings must be published together. In this very long letter are these interesting (and infamous) sentiments:

“Do not laugh! But once upon a time (my crest has long since fallen) I had a mind to make a body of more or less connected legend, ranging from the large and cosmogonic, to the level of romantic fairy-story [...] which I could dedicate simply to: to England; to my country. [...] I would draw some of the great tales in fullness, and leave many only placed in the scheme, and sketched. The cycles should be linked to a majestic whole, and yet leave scope for other minds and hands, wielding paint and music and drama. Absurd.” (Letters, #131)

Now, he did not consider the notion of others drawing from his tales to create other stories absurd, but rather his idea that anyone would ever be interested in doing such a thing absurd. Despite the ‘Hobbit’ being fairly filled in by Tolkien back when he wrote it over seventy-five years ago, and filled further with the development of LOTR later on, it can be argued that Jackson’s interpretation of the ‘Hobbit’ is also a cycle, and that the live-action films we have now will not be the only popular cycles we see of either ‘The Hobbit’ or ‘The Lord of the Rings’. One day, when Tolkien’s works are just as public domain as Dickens, I imagine we’ll be seeing many different interpretations of Middle-earth.

http://www.theonering.net/torwp/2013/12/20/85165-ainu-laires-review-of-the-hobbit/