SI has gotten more rookie-heavy over the past few years. I like it, 'cuz I was getting a bit sick of them having the same models over and over, such as the fact that Heidi Klum was in it eight years after her 1998 cover.
Not all the rookies are my cup of tea (I don't get the appeal of HF models like Cintia), but to each their own, and I appreciate the spirit.
I think Brooklyn would work very well on the cover because she has much broader appeal to the SI demographics than other models: she speaks with an understandable American accent and knows her football, so the multiplier effect of being on the cover is much higher. It's the same reason why the cover worked well for Marisa. Having a non-US model isn't necessarily awful, but it's almost a waste of the PR coverage (as unfair it is to them).