I still think that they're just going to make Quicksilver and Scarlet Witch Inhumans in the MCU. In the Winter Soldier post-credits scene, Strucker and his lackey were talking about how all the other test subjects they'd been experimenting on had died, and only Wanda and Pietro survived the process. I'm thinking that's because their DNA contains latent Inhuman genes, and Strucker inadvertently activated those genes and triggered the twins' powers.
Kevin Feige was talking about how much he wanted Inhumans and in the same conversation said that Quicksilver and Scarlet Witch would not be Inhumans in the movies. Given that context, I can't think of any reason to be deceptive and he certainly was unequivocal that they would not be Inhumans.
So I really think this belief has been thoroughly debunked by now.