How often do clients ask agencies for it?
And how often are they then disappointed when the agency fails to deliver?
Robert Senior of Saatchi & Saatchi Fallon Group makes a very good point or two in Campaign, to quote: "There are very few big ideas - and the really big ones had no sense of their destiny at birth." It's quite true - huge oak trees don't just appear overnight. His advice to clients when assessing work is, therefore: "Ask not 'Is this a big idea?' but 'Could it become big?'"
On the media-neutral question, my son asked me recently which came out first, the Star Wars films or the Star Wars books? Star Wars started life, as far as I know, as a film (or at least a screenplay), but it didn't have to. It's a media-neutral idea, along with Pirates of the Caribbean, which started life as a ride. Either of these could have started life as a game.
Just because an idea comes attached to a particular medium when you first see it does not detract from its media-neutrality.
Looking forward to an acorn or two in the next agency meeting!