I'm trying to think about this logically based on her previous set lists so here are my thoughts...
I think she will start with a happy, upbeat song that is not the title track because on the Fearless Tour, she opened with You Belong With Me and on the Speak Now Tour, she opened with Sparks Fly. So eliminating all sad/angry songs, slow songs, and the title track, our options are Starlight, 22, Holy Ground, State of Grace, and Stay Stay Stay.
I think Holy Ground and Stay Stay Stay are not popular enough to kick off the show because she'll want to begin with a song that everyone knows and not everyone at her show is going to know all of her songs like we do on TC. 22 is very different from her usual style and deviates quite a bit from her country roots. While she is moving over to the pop side, I don't think she'll want to start off so different from her original style. That leaves State of Grace and Starlight.
In my opinion, Starlight would make an amazing closing song because the song even says "the whole place was dressed to the nines and we were dancing, dancing like we're made of starlight." That is in the past tense and therefore, it makes the most sense as a closing song rather than an opening song. On the other hand, she always closes with a song from the previous album (on the Fearless Tour, she closed with Should've Said No and on the Speak Now Tour, she closed with Love Story), so I don't think she'll close with it either. If I had to guess, I would put Starlight towards the end, but not the very last song (like where Long Live was during the Speak Now Tour).
Since I think Starlight is unlikely, that just leaves State of Grace. So like many other posts have suggested, I think State of Grace is a reasonable guess.
If I had to guess her closing song, I would say Long Live or Mine because they are upbeat, happy songs from her previous album. Long Live is symbolic and Mine is popular so I think it could be either. I don't think she'll close with Sparks Fly because she opened with it last time.
Wow this post is so long! We'll see if any of it makes sense haha!