Sometimes I've found it very useful to start plays outside New York, where you can actually see if the production is fully realized. Three Days of Rain we did at South Coast Rep, and it was very successful, but it was a four-actor play. And we brought it to New York, it became a three-actor play, as it needed to become, but there's no way you can know that without a full production. I don't think it's only a place where finished products can be shown. Look at the Public, the Vineyard, Playwrights Horizons.
Theater companies shift and grow.
The Public is now something of an elder statesman, and new companies emerge with the energy you're talking about. So the landscape continually shifts. And that's healthy. That Sam Shepard energy is still alive in the Downtown avant-garde world. But the focus has shifted from the playwright to the director.