According to PWinsider, One of the reasons WWE is doing a Sin Cara vs. Sin Cara feud is because Rey Mysterio is going to be out with an injury and they want to do something big around Lucha masks for WrestleMania next year in Miami. WWE has it on their agenda to break the Guinness World Record for the most masks in one place, and are looking to do so in Miami.
The new Sin Cara (Hunico) was the second Sin Cara to come out on RAW last night. One of the ways to tell them apart is the original Sin Cara (Mistico) has the blonde hair sticking out from under his mask while the new Sin Cara has a scar on his stomach.