Events of the past twenty years or so lead me to believe that the multi-religio/ethnic nation-state will become a thing of the past.

I do not see a consolidation into a one or two world earth; I see a division back to what is essentially tribalism. For instance the sundering of nations in central and eastern Europe along ethnic and religious group ties has already occurred. Africa has the problem of Sudan (this thread), Eritrea and other problem areas...e.g. I'm not sure the Tutsi/Hutu problem is fully resolved. In Iraq, Druze, and Assyrians would welcome separation from the general Moslem populace. Some Druze would like to incorporate parts of Turkey and Syria, wherein reside large numbers of their fellow Druze. Of course, we've discussed the Israel/Palestine problem ad nauseum.

Political pundits speak of the USA as a nation divided, and some think Mexico is yearning to reclaim the southwest United States. Indian tribes are considered sovereign nations immune from much Federal, State and local control of the area surrounding them.

Quebec periodically rattles the sabre of secession from English speaking Canada.

While the list is not complete, nor is tribalism likely to reach its apex in my lifetime (what's left of it), I believe it to be a real possibility.