Alot of that depends on what the church will look like. What will the church look like? Barna has done some research and is writing a new book. Here are some reviews of an advance copy:
"Revolution", George Barna's new book, will be published in September. Barna leads a church research institute, and is currently the most-quoted person in the Christian church in the USA because of his statistical work. To summarize the book's most important conclusions:
* The number of Christians attending local church in the USA is declining rapidly. Today, 70% of Christians attend traditional churches, but this will sink to 30-35% in 20 years;
* The number of followers of Jesus who do not attend a local church will grow from 30% to 70% in the next 20 years;
* Alternative fellowship forms (house church/simple church, post-modern churches etc.), currently home for 5% of USA Christians, will grow to make up 30-35%; another 30-35% will live out their faith in the fields of media, arts and culture; the remaining 5% of Christians attending non-traditional forms of church will have a family-based spiritual life;
* Conclusion: a minority group presently not even noticed by many will become the mainstream of North American Christianity in only two decades.
http://sojourner.typepad.com/house_church_blog/2005/09/the_new_revolut.html
http://sojourner.typepad.com/house_church_blog/2005/09/more_barna.html