Assimilation, the idea that small numbers of migrants, very gradually come to integrate into a dominant culture, and then blend in, is one of the great myths of liberalism. It has been debunked, first by recent Islamic immigration, not only with home-grown terrorism: http://edition.cnn.com/2016/06/12/opinions/orlando-homegrown-terror-bergen/, but also with the process of endless chain migration which has now been set into motion: http://www.dw.com/en/report-nearly-one-in-two-muslims-in-germany-engaged-in-aiding-refugees/a-38137761, and its dispossessing effects upon the dwindling numbers of locals: http://gatesofvienna.net/2013/05/everything-you-have-learned-in-school-is-wrong/.
Secondly, the assimilation thesis is defeated by the sheer numbers of migrants which have completely transformed Western society. Australia, in particular is paraded as a “successful” multicultural society because the elites have been completely able to transform its Anglo-Saxon basis, 99 percent at Federation, to one where nearly half of all Australians, which only has a legal meaning, were either born overseas or have at least one parent who was: http://www.dailytelegraph.com.au/australias-demographic-details-will-shock-you-almost-half-of-us-are-foreigners-or-their-children/news-story/7ae164c13cf15f7e9b5d3ee7c6465816. This is “successsful” because the transformation was done without a civil revolt, because of the deracination of Anglos and white pathology, something which needs discussion all on its own. It is not “successful’ considering the ethnic interests: https://en.wikipedia.org/wiki/On_Genetic_Interests of the displaced group, any more than Aboriginalists see their displacement as “successful.”