I've heard Steve Hayner of Columbia Seminary speak a couple times on the missional idea. Here's a article from the Presbyterian Outlook that he wrote that sort of sums his perspective.
This way of thinking about how to “do church better” hasn’t worked. The Church in the West is dying. Europe is now “post-Christian.” The Church in the U.S. has not grown (in percentage) in more than 100 years. And many denominations, including our own, are falling precipitously. People are no longer inspired by or attracted to institutional religion. The church is being pushed to the margins.
The question is what model or methodology is best suited to turn this around. I'm skeptical of many of the contemporary models that seem to be based on old models, just restyled for a new generation.
I believe the missional idea is a key one for revitalization of the church. That said, I don't think it is as simple as it might appear. After all, you may say that your church has supported missionaries and local outreach missions for years. Isn't that what missional means? Yes and No.
Yes, in that it is about reaching out beyond the circle of the congregation. No, because it isn't really about doing another program. It goes deeper to the church's whole orientation to what its purpose is.
It is analogous to those churches of a traditional form that took the radical step of adding contemporary praise music with a rock band to the service. In the end, what they did was slap a "new traditional" veneer on what they had always been doing. It was a reorientation. It was Extreme Makeover: Worship Edition.
The missional concept has strengths for the mainstream church because it is about the church turning from an inward focus to an outward one, and being open to where the Spirit of God will lead when they begin to see opportunities that they missed in the past.