I believe there is and will always be role for the mission agency: a structure able to take people from one continent and send them to another. The role is important, but may be limited by expense, passport issues, and risk.
I have long been thinking about a slightly different structure – the “mission society.”
There is a “last mile” problem that non-local mission agencies can’t easily crack: we want local churches to be key to local evangelization, but if there are no local churches, and non-local missions can’t get into a particular area, what’s the answer?
The answer, to me, is a “mission society” spawned out of the local church and able to go that final distance.
Churches are “E-1” – evangelizing in same language, same culture.
Mission agencies tend to be “E-3” – crossing barriers of language, culture, etc.
“Mission societies” – this structure I am envisioning – would tend (probably) to be “E-2.” They are crossing cultures, but remaining largely within the same geographic and linguistic family. I am envisioning them as being far more lay-inspired and lay-led. Bivocational. Local. Decentralized. Rapid. Mobile. Close enough to the target culture to understand it without 2 to 4 years of language and culture acquisition; far enough out that crossing a cultural boundary is required. Able to be something of a bridge between E-1 (local church) and E-3 (agencies) that are involved.
I suspect, even though they may not be called such, this type of organization already exists, and in great numbers. They are sort of the “long term” goal of any church planting movement – the structure that a movement “births” to hop a linguistic, cultural or border barrier and spread the Gospel into a nearby people group.