Did JRRT encourage new ME stories?

[Sauron the White]

I asked this question

What will happen when the copyrights begin to expire?

and was provided with this answer:

I'm sure the vultures will gather & wring every penny out of Tolkien's genius they can.

Please allow me to ask this again and to say I am looking for something more fact based and less of an editorial comment.

At what point in time does the copyright lapse on any of the Middle-earth based tales?