Maybe if with new rights they could get the clout that say JK Rowling has over the Harry Potter movies they might release parts. I think Aldarion and Erendis could make a great film as one of the stories with real passion. I doubt they would ever just sell the lot - so much of it is undefinitive.
Of course since they are hamstringing the Hobbit to fit in with LOTR it may be closer to the Quest of Erebor .... and the quest for the ring will surely feature in the hotchpotch movie ... but thinking about that is far too depressing
I adore UT for all the extra information but I am not sure that there is much else that would really have enough for a stand alone movie. The Narn and Tuor are not complete in UT, Does the pact of Cirion and Eorl have the impact alone? If you separate it from its fulfilment at the Pellennor? If you remove the Disaster of the Gladden Fields and Orophir /Thranduil at the Battle of the last Alliance from the wider history of the Rings of Power is there a movie in them? Not sure.... wonderful episodes if you were doing a great epic tv serial but maybe not a film.