The AR demo was really cool, especially for a miniatures lover (still not seeing THAT widespread...can't play in bed, etc...) and the iPhone X screen looks impressive but....the no home button gestures, unless you can disable them somehow, are going to be a nightmare when gaming.
To me it certainly looks gimmicky. I cannot think of myself truly enjoying AR games like other games when I always need some kind of flat surface to move around. As you mentioned playing in bed is impossible, as is playing in transit or generally on the go outside. Even at home while just chilling on the sofa it might be difficult if you do not want to get up.