I've had this idea for a bit, not sure if anyone else has thought of it...

But what if when TD was pulled into Equestria, it wasn't him that gets pulled through, buts instead his sister, Kristen, gets pulled through? Like, she decides to stay with him for a few more minutes before heading off to class, sees him about to be run over by a car, pushes him out of the way, and consequently Celestia pulls her through instead of TD?

I kind of want to write this, but I'd need to fine-tune the idea first and I wanted to run this by a few people.

Depend of how you write it, I think it could be a good idea.

4439360 It'd be hard to pull off and appease the fans. But it could end up OKish. Though after the start it's it's own HiE - completely separate to the non-bronyverse in most ways. There is potential for some interesting future conflict. Though, would his sister punch Celestia in the face...

I'd read it.

Depends on what she's like but I'm fairly interested. Going back to the simple beginning with a twist sounds fun.

4439360 ask the master himself. maybe he would have some pointers.

But what would be the difference between TD and Kristen? Don't they essentially have the same personality?

Hmmm, well...
Coming from you, I'd read any work you create. I'm sure you could bring life to the idea of her getting transported instead of TD.
Sorry I can't offer much more than that little piece of encouragment