and I know other fantasy works, like Pullman's His Dark Materials, have had some success in play format.

Maybe that wasn't what you meant, but then it's not entirely clear to me what you did mean... while lots of plays are set in somewhat supernatural or fantastical settings, it doesn't make much sense to me to write a (new) play that resembles a fantasy or sci-fi novel in terms of worldbuilding and the like. Any good play is mostly about the characters and their interaction, as evidenced by the popular concept nowadays (actually, it's been a popular concept for centuries, I suppose) of taking old classical stories and plays and putting them in a contemporary setting and decor, rather than striving for historical accuracy in the costumes and decors. Jesus Christ Superstar did it, Luhrmann's Romeo + Juliet did it, and more theater productions than you can see in a lifetime (that may be slight hyperbole, but not by that much, I don't think ). So how/why write a play that focuses instead on creating a fantasy or sci-fi setting?

As for your statements about there not being SF/F cinema that you can take seriously after 1990, those are fairly baffling. In the top twenty of highest grossing movies ever on IMDB (not adjusted for inflation, but then we're only talking about after 1990 anyway, which all twenty are), I count eight fantasy movies, four sci-fi movies, seven other movies with fantastical or supernatural elements of some kind or other, and exactly *one* that doesn't have any of those elements (Titanic). Now if you disregard blockbusters and only focus on more critically acclaimed movies, the picture does change a lot, but still there has been acclaimed fantasy and sci-fi - just look at this year's District 9, for instance, or Pan's Labyrinth of a few years ago. And on television, there are almost too many shows to count - everything Joss Whedon, Heroes, arguably Lost, Doctor Who, Battlestar Galactica, are merely the first bunch coming to mind on a very long list.