I don’t remember anywhere in the keynote where Craig Federighi reminded people that Memoji only works with the iPhone X. It does say so on Apple’s website but how many people go there to get details? I expect Memoji will be very popular, I’m already seeing tons of people’s Memoji’s on instagram. But I doubt many kids or teens are rocking an iPhone X. I can see there being a lot of disappointed teens thinking this will work with their older device and finding out it doesn’t. And I don’t think parents are going to rush to buy a $999 X for their kids. Perhaps this signals a cheaper iPhone that will support these features is coming?