I've found rather the opposite, that second generation Muslims tend to be quite secular, or if pious, very comfortably integrated in general society. There's a spectrum, but I see very little entrenchment in second generations.  There's no reason to believe what has happened to every other previous immigrant group, wont' continue to happen.  

Muslim population growth is increasing linearly, not exponentially. If you take in one million a decade, at the end of the second decade it will have "doubled" to 2 million, but it won't' double again to four by the third, it will increase to 3 million linearly. Aboriginals have very high natural growth rates and will continue to outnumber them.