I honestly don't think genre matters that much.
I just think She needs to show there is something more sophisticated than SIO on the album for fans who aren't into SIO

Plus every promo single, regardless of genre or lyrical content, generates a lot of promo (on music news sites, on tumblr/twitter/forums, people on iTunes saying "why are there 3 Taylor songs in the top 10?" etc.)
Maybe we won't get any, but it seems weird that She would abandon a practice that has worked SO well for Her.