Star Wars: The Last Jedi - 8 Parents J.J. Most Likely Wanted For Rey
6. She's A Clone Of Luke
In what is now referred to as Legends (formerly referred to as the Expanded Universe) decades of extraneous Star Wars material is cataloged. This includes any and all books/comics/video games that were considered canon before the Disney buyout occurred, and have been de-canonized since.
In one such storyline, the Empire retrieved Luke's severed hand that he lost on Bespin at the end of Empire Strikes Back. Using the cells from it, they created a clone of Luke Skywalker. In Legends, this clone was named Luke Skywalker. And no, that's not a joke.
It isn't hard to see why Abrams might have considered this option.
Abrams and Kasdan set the precedent for borrowing from Legends to create new storylines in Force Awakens, with characters such as Kylo practically being ripped straight from the source, just with a name change. They also make a point of having the original Skywalker lightsaber return to the fold, leaving the question open as to what became of Luke's severed hand or how Maz Kanata even got it.
This is the kind of thing Abrams has loved to do throughout his work; leave multiple threads dangling before tying them all together.