Alright, so now that our internal rage has been released, let's talk about this rationally (And by rationally I mean stuff that AmourShipper_ pointed out because I was kinda sorta busy raging).

1) Serena is SMILING.
Alright. They boy of her dreams has been stolen by Miette and she seems happy about it. Either Miette and Serena have devised a plan or:

2) It is likely that this is a ballroom dance.
Ok, so if it is a ballroom dance, then the participants would rotate partners every now and then. And if Serena is smiling then either she just got done dancing with Ash (She would probably be a little more ecstatic than shown) or hasn't gotten the chance yet and is waiting for that chance. I am a little surprised that she does not seem nervous (but then again this is only a moment) but maybe that little confidence boost really has taken over her fears and everything.

3) THIS IS A "Satoshi and Serena!!" EPISODE.
There has to be a dang reason why this is in the title. If they change it to "Satoshi and Miette" or "Serena and Citron" (They definitely won't do either of these), then this picture makes sense. It was also around this time that the "date" episode came out last year, and we can assume that late January/early February is XY's little "Amourshipping Episode Day".

Let's not freak out yet and wait for more previews.

(continues thinking nonstop about this episode)