Mark Hamill even dropped hints that Rey was NOT his daughter recently. Plot wise it makes perfect sense. Someone wants to breed a new chosen one. A new Anakin Skywalker for the New Order. Rey was one of the rejected clones that was abandoned on a desert planet to hopefully create Anakin. As for how they got Shmi's DNA, that's easy, Palpatine/Plagueis probably had her DNA on file for years along with all the other humans they experimented on. Also remember Luke's line from ROTJ. "I never knew my mother..." well now we have a space age twist of him actually getting to know his grandmother years after the fact! And look at the facial similarities. This was not unintentional on Disney's part. They even have the same style of clothes. Shave 30 years off of Shmi and you have Rey. Mystery solved.
Despite being 35, I've never driven a car in my life. But I'll throw in my fiances car, though. She won't mind.
I doubt that Disney will base the origin tale of one of the most popular and well received characters of the franchise on the cloning of a character who has 20 minutes screen time at the most, 19 of which were in Episode I. I suppose it is plausible in the 'anything is possible' sense, but I doubt they are going to gamble $4bn or any part of that figure on such out there plotting.
If Rey is a clone of Shmi, I think all the shippers can agree that either Kylo or Finn would be a big step up from Cliegg Lars.