I think bonnie will do the exact opposite and try and get Serena with his brother
Since I think the running gag will be most likely Bonnie trying to convince every around-her-brother-age girl they bump into to get together with her brother, that would be not the case.
Maybe the first time they meet, then I can see Serena politely refuse the offer, cause she has a crush on Ash. If Serena tells her or Bonnie realizes about that I doubt she would interfere with it anymore. In fact, chances are that Bonnie'd become a SatoSere fan and would try to get them together and tease them, while still trying to get her brother a girlfriend lol
Anyway, we don't know if Serena has a specific and active goal yet, or just a passive type of goal, (c'mon, even Misty was just following Ash because of her bike in the beginning and May didn't know what she wanted to do), maybe she just wants to travel for the sake of it, or what would be great for us , she just wants to travel with the boy she met when younger.
I think the rival talk should wait until then, if there is any. I was just proposing it to see how you think the characters would react and making things a bit more interesting, Serena looks like a nice and kind girl, so most likely a mix of jealously and sadness if a girl, and Ash acting the way he did with Rudy and Misty if a boy, this time not because he is being ignored but actual jealously, but I can see Ash not realizing why he feel that way. lol
In any case, it could be Ash's rival too,boy or girl, or anything really, as Graham Aker said there could be lots of variables to "disrupt" the shipping, but we better not talk about them ahead of time.
But one thing is for sure, this shipping has solid bases, even more than Poke-Advance-Pearl ever had, the fact that they actually are making some things different should make us stop reflecting this ship with past ones, to a certain degree at least.
In other words, it will be exciting to see how all this unfolds.