This is a *SPOILER*, but I just saw the TLJ Luke Funko Pop for September has this spoiler, so I'm sure it'll probably be officially revealed by Disney sometime before the movie is released. But of course, read on at your own risk.
So Luke apparently has a necklace with a fragment of Darth Vader's lightsaber crystal and it plays a part in the plot. I find it very hard to believe a piece of Vader's saber could be recovered as it fell in the Death Star reactor that was destroyed moments later. Not only that, it kinda takes away some of the significance (for me anyway) of the Graflex, being a special Force relic of a bygone era. Perhaps it's a symbol of Luke's dark side?
Also, someone get me a Porg.