I think the sabre hidden in the rocks should be Ben’s. The one we see in the flashback in TLJ. It could be easily implied that he abandoned his sabre after destroying the temple, and Luke found it and hid it the walls of his hut. Metaphorically, Rey repairing Luke’s mistake. Also, it’s as if the force is aware that Ben has turned and his calling for his sabre to be returned to him.
The tricky think is Ben uses Anakin’s saber throughout the third act, while Rey uses Leia’s. It would take a lot of work to swap out the hilts for every shot.
That’s a very good point. Though if someone could accomplish it, I think it would be the best option narratively and tie the film in a little closer with TLJ and make the three films seem a little more cohesive.