When people say, "we need better people group lists," it nearly always comes from this sort of thinking:
This leads us to the idea "some from every ethne" before the throne is enough. This is poor missiology.
If the goal is "some from every people group" based on heaven's list of peoples, then we need a better list - but we may have failed in this already. Many peoples have already disappeared.
But I don't think Jesus was saying 'I want some from every people group.'
I think Jesus was saying, 'I don't want any people groups left out.'
Jesus wants it all. "For God so loved the world... that none should perish." Jesus wants The whole pie.
I don't mean that everyone will respond. We know not all will. But we ought to be tilted toward Jesus' desire, which is all. Even if they might not all respond.
(Yes, I know there are theological statements involved there. No, I'm not going to go too deep into them. Let's keep this at the simple level of John 3:16 for now.)
If the goal is "all," then the task of researching people groups is really pretty dramatically simplified.
What we need to do is reach everyone within each particular geographic segment (every country, every province, every district, every subdistrict, every city, every village, every rural collection of farms, every desert, every tropical jungle, every river, every every) - and we need to do enough research on the peoples inside the segment to make sure that no individual is cut off because of their language or culture.
People group thinking is important only insofar as it identifies barriers to the Gospel - not important as an "end goal" of the task.
Here's another, simpler strategic approach: work on reaching everyone in a particular area. Monitor the growth of the church. When growth stalls, look at the people who are not coming into the church. Research their ethnicity, language, culture, sociopolitical affiliations, lives. Get to know them. Find out what the barrier is, and craft away over the barrier.
We don't need better people group lists; we need a church committed to loving, reaching, inviting, blessing every person.