I read this Blog with great interest, as you bring together in a short space a number of important points.
Two additional topics are worth pursuing. First, the migration thresholds in receiving countries; beyond a certain number of immigrants, their social and even economic integration becomes more problematic. There is a growing body of literature on this.
Second, the circulation migration; a lot of current research looks at migration as one finite step, moving from A to B, whereas migrants can actually circulate (going back and forth several times) between A and B. Actually, this might be one the key policy paths for the future.
The Population Reference Bureau has just published "The Global Challenge of Managing Migration", a new Population Bulletin (see www.prb.org).
John F. May
Population Reference Bureau