I imagine Mies would not have been pleased to see Jeff Koons's kitschy pink balloon dog standing guard in the lobby of the Seagram Building, his masterpiece of pristine austerity. Philip Johnson? You've got to figure he would have smiled at the juxtaposition. It would work better without the plinth/velvet ropes, but there's something about the object and its formal simplicity (prettiness?) that fits.
If you were inclined, you could write a thesis on the nature of art, commerce, and cynicism inspired by the combination. A largely unknown fact: Mies had actually planned to design a pair of sculptures to sit in the two pools in the plaza of the building, but eventually decided against. Just imagine a pair of Koons dogs in those pools, standing sentinel like Patience and Fortitude at the NYPL. For what it's worth, here's Susan Sontag (chief theorist of kitsch), and Philip Johnson (sometimes practitioner thereof) in conversation about the Seagram Building. Too bad they're not around to comment today.