Guys, don't give too much attention to their physical traits (height,skin,eyes,teeth,etc). Remember that they had new artists and they have their own style of drawing. They also doesn't seem to give much details on how their heights look or how tan their skins are. That's why sometimes you see Serena taller than Satoshi and vice versa.
As for the yandere part. Yeah, it's just a joke, don't take it seriously.
Also, some people say that if ever Iris reunites with Satoshi and if she calls him a "kid", Serena would be mad at her. Personally I don't think so. She would just probably laugh it out on how silly they look. I mean how bad does it sound anyway? I haven't seen BW quite honest but is it really that bad that Iris calls him a kid to the point that it would totally offend someone?
Serena being taller than Ash is just an optical illusion. Her hat seems to be bigger than Ash's.
And I think Ash looks taller because of his clothes, which makes him thinner and therefore taller.
Well about Iris. Calling Ash a kid almost every episode was really annoying. Maybe that was OK first five time. But after 100 episodes it became really old and boring. And when Dawn also caught that. That was very low.
I don't think the writers would want to ruin XY by bringing back Iris. She was afterall, the most annoying companion Ash ever had.
I know it's a trend but I wouldn't like to see her again in XY. Instead, they could bring back Brock for a few episodes.
I think better chances of return has May. Hoenn remakes, May's love for romance (and Kalos is based of France with Paris, the city of romance). Iris has no good reason to come to Kalos and unlike AG or DP when Ash got his main travelling companion. Iris acted more like another Brock along with Cilan.