Ok, my thoughts are getting away from me. Let me write out my basic theory of the plot, stream of consciousness style.
Luke's hand/lightsaber fall into Bespin trash.
Someone finds it and hands it to Cloud City lost and found, or the Empire confiscates it.
Lando grabs the saber (making its way to Maz), Luke's hand makes its way to Palpatine.
ROTJ happens, Palps dies.
*A few years go by*
Snoke somehow uses the hand to create Rey.
Rey is purposely abandoned on Jakku, in an attempt to force her into her own "Luke's hero arc" that will eventually unlock her full force potential.
*Decades*
TFA and TLJ happen
Rey, still trying to make sense of her origins, somehow discovers that there is something important on the Death Star II. (Maybe via Lando)
Rey discovers Death Star II wreckage contains map to what turns out to be the cloning facility where she originated from. (And surprise, it's on Jakku.)
The big reveal - Snoke was [perhaps unknowingly] a puppet for Palpatine. Snoke is not the clone of Palpatine as she suspected, Rey is the clone. Palpatine was the puppet master behind everything, who put Snoke on the path to cloning Rey.
I still can't figure out if Palpatine is physically alive or just influencing Snoke from the "beyond", ie as a dark side force ghost.