I saw Fairview in Brooklyn. Although it's true the white audience members weren't compelled to go onto the stage in the last scene, there was certainly a sense of obligation. I dutifully went up on the stage, and found it very uncomfortable (which was I assume was the point.) But the black people in the audience also seemed extremely ill at ease, with a big clump of white people staring at them.
It's interesting that the Pulitzer committee, who awarded this play their award, only reads plays in their written form. They never actually see the play in action. I'm sure reading in the script that white audience members are expected to troop up on the stage has a different effect than actually participating in it.
That said, there is a lot to admire in this play. But the thing I remember most is the segregation of the audience at the end.