Copyright your book or story, and offer it to the studios. They have screenwriters who will convert it to a script.

Oh, it gets complicated when many people start typing on the same page. Despite whatever agreements are made by registered users, it's difficult to tell who is truly responsible for the writing: the guy with the idea or the dozens of others who altered it along the way. There's also no guarantee that a sold script will actually make it into production—many studios keep databases of scripts, some decades old, that may never be looked at again. Finally, others can exercise clout and have the script rewritten any number of ways.

One area this might aid is the issue of copyright. A wiki format in particular can be very aggressive in documenting how a script is developed, down to every added dot. Another way this could help is to instruct people on how to write a good script, and what makes a good story. There are plenty of websites that go over details like these, but the common ground on "breaking in" seems to be having the guts and genius, and just talking to the right people.

Screen writing is such a strange craft few really understand it and most of those are working in Hollywood and New York. Leave it to the pros. The people who buy scripts do. Poor idea and the stuff of which really stupid pictures are made.