The article is well written and has taken an alternate view to the trend, which can be said as sad. I believe there is a lot of truth in this one actually over the former views that European muslim population was exploding, one that I admit I was personally adopting.
However, I have an argument against one idea, perhaps personified by this sentence:
The other problem with forecasting numbers of European Muslims in 2100 is the presumption that sixth-generation European Muslims will still be a foreign body here: Islam as a bacillus that even secular former *Muslims carry around, forever dangerous. This ignores the transition affecting many nominal Muslims in France.
While this was basically true for a long while, no one can downplay the recent surge in the return to Islamic values ALL OVER the World. In Egypt if someone was wearing a veil in the 70's, they would be stared at like an outer space alien. Ardianto I believe was the one recently telling us that Indonesia until recently had a strong secularist government, and today Islamic notions are rising everywhere. Turkey was as secularist and even more unislamic than European countries (veiled women were forbidden) except the last period: veiled women came into office, ties with Israel are being broken, and attention to their Islamic identity is resurfacing. I heard of 20 friends of univeristy and old times, who either started practicing, growing a beard, or got involved in scholarly work rather than having been just wasteful youth.
There is a definite trend that cannot be controlled, where it seems the information spread and societal norms have revived the Islamic message and practice amongst its people, and no matter how many generations a muslim family is in Europe, if new reverts are practicing, then a vast number of those muslims will maintain their identity and religion.