Possibly, though it's unclear precisely what...
Amazon announced in November 2017 that they had struck a deal to produce a television series based on Tolkien's works, and specifically mentioned the Estate1:
Amazon today announced it has acquired the global television rights to The Lord of the Rings, based on the celebrated fantasy novels by J.R.R. Tolkien, with a multi-season commitment. The upcoming Amazon Prime Original will be produced by Amazon Studios in cooperation with the Tolkien Estate and Trust, HarperCollins and New Line Cinema, a division of Warner Bros. Entertainment.
It's not currently clear what role the Estate actually had in these negotiations; one possibility is that the television rights didn't fall under the scope of Tolkien's initial deal with United Artists, in which case they would seem to have sold them (or at least licensed them) now.
Another possibility is that they sold or licensed parts of Tolkien's unpublished drafts; the press release asserts that the series will be a prequel of sorts to The Lord of the Rings:
Set in Middle Earth, the television adaptation will explore new storylines preceding J.R.R. Tolkien's The Fellowship of the Ring. The deal includes a potential additional spin-off series.
Obviously details are scarce, but it's possible that these storylines will be based on material only published in Tolkien's essays, the rights to which had not been sold in 1968.
...but otherwise no
It's difficult to prove a negative, but aside from this deal (and whatever involvement the Tolkien Estate had in it), at time of writing there is no evidence that any other Middle-earth rights have been sold since J.R.R. Tolkien's initial United Artists deal.
What I have for evidence is as follows:
As FuzzyBoots remarks in a comment on the question, the Tolkien Literary Estate (through Christopher Tolkien, sole literary executor of the estate) has been extremely critical of all adaptations of Tolkien's work (particularly the Peter Jackson films). That they would choose to sell the rights they have left seems unlikely, given this history
The Estate has fought to keep the scope of the rights owned by other companies as narrow as possible; in 2012 they sued Warner Brothers over digital merchandise (in particular, an online casino gambling game), to the tune of $80 million; this suit was settled in July 2017.
As I've pointed out before, the Estate isn't interested in so much as licensing the rights they currently have, let alone selling them
In a 2014 press conference, reported on by Variety magazine, Peter Jackson outright said as much (emphasis mine):
"It's a legal thing. The Tolkien estate owns the writings of Professor Tolkien — The Hobbit and the Lord of the Rings were sold by Professor Tolkien the late 60s... the film rights," he said. "But they are the only two works of his that have been sold. So without the cooperation of the Tolkien estate, there can't be more films."
1 Sidebar, but I find it interesting that the press release mentions the Tolkien Estate and HarperCollins, who hold the literary rights to Tolkien's works, and New Line Cinema, who hold the intellectual property rights of the film material, but not Middle-earth Enterprises, who hold the actual film rights.
My instinct suggests that my first guess was correct, and that Middle-earth Enterprises in fact did not hold the television rights to the stories. But I'm not a lawyer, and I'm not an insider on this deal, so I don't want to come down hard on that point.