I am really enjoying this. I hope you plan to continue this story.

This is a guilty pleasure, I admit. All the same I hope it has a satisfying conclusion, what entertainment is there (beyond our sick fetish) in having our beloved characters get into trouble with no way out?
I can see a couple of the mane six accepting a fatter them, but that doesn't mean they just give up. Pinkies the obvious choice for not having a problem with this, while I can see Rarity continuing to brush her coat and serendipitously work out to sculpt her fat into a more pleasing shape. "I may be a cow, but I'll be the most stunningly beautiful cow in Equestria."
Twi is more concerned with her mind than her body, so she might only find bulking up annoying (or pull an L, "I require a high sugar diet to maintain my keen analytic mind.") while she continues to observe to learn what's going on, maybe antagonizing the Stuffer into revealing some things if she's clever. An aside, has it been explained if they can't use magic, thus why Twilight isn't blowing down walls and teleporting?
Fluttershy will be more concerned for the others than herself, but I think she takes a lot of pride in her natural beauty and might flutterrage if a viable target presents itself. The athletic AJ and RD are the most hurt by the Stuffer. Applejack's set her identity on being dependable for her family and friends, how dependable can she be if she starts breathing heavy just walking around the room. Dash is even worse off, as illustrated; she IS the fastest Pegasus alive, becoming an immobile mass is going to weigh (hehe, pun) on her more than most.

The mystery coupled with the decent writing has gotten me really curious as to where this is going, I hope their is some more to this than shameless chub fetish. Not to demand you change your story if it is, I'm along for the ride, even if I'm not a fan of morbidly obese immobile ponies.

I'm ready for the next chapter

Can't wait for the next chapter

pinkie knows too much about the traps of the room plus that static guy says that his boss has great contacts and pinkie knows everyone in equestria so im saying pinkie is the bad guy

Love the story! still hoping for an update.