What is the biggest barrier to the wide use of plain language?
Lawyers need to develop new writing habits. That is all. Once you have learned to write legalese and you have done it for years, it is ingrained in your thinking patterns. I have been working at plain language for 19 years, and still, my first drafts often follow traditional legal phrasing and sentence structure, and I have to think twice about word choices. So make that two things: develop new writing habits, and allow yourself enough time for each writing project to do it right.