Not a bad idea--and one that is going to minimize the number of immigrants, since Dutch is a notoriously difficult language to learn! In order to pronounce it properly you must first stick a herring down your throat and choke on it. I don't see these Muslim immigrants tackling that; where, anyway, would they find someone to teach them Dutch in advance of going to the Netherlands?
Good for the Dutch. I love the country but for years have been disgusted with the left-wing views of the Dutch people and government. Looks like they've begun to change their collective mind.
When I was in the Netherlands years ago, people there told me some folklore (who knows if it's true) that during times of war, in order to detect who was truly Dutch and who might be an enemy infiltrator, if there was any doubt about their nationality, the soldier would be asked to pronounce the town of Scheveningen.
Only someone who grew up speaking Dutch can say it properly. I couldn't even begin to say it right, but came close when I pulled my tongue all the way to the back of my throat, spoke through my nose, and said "shaving". That got a chuckle from my Dutch friends.