If someone can get a hold of that exact plush, maybe we could have a real live Pinkie Pie roaming around! We just need to come out with technology to deplushify living creatures.
If it’s the balloon thing, innocent play always comes first. Interacting with them in itself is not the fetish. That would depend more on how the individuals perceive / treat it.
As it is, it’s just a tame bit of eye-catching party-tastic fun (that some might like more than others) and probably not meant to imply anything else.
If it’s the TF thing, then I have no idea? But I’m pretty sure the balloon bursting thing is just done for an easy screen-wipe transition, just like in the show’s intro. “Tons of fun!”
I love how she looks slightly shocked when the balloon fills the screen, almost as if she’s thinking “What? But the balloon is supposed to break and then we cut to Rarity tossing her mane!”