Good question. Some thoughts on the Flynn effect:
1) It is environmental
The Flynn effect is caused by advances in environmental factors, particularly in prenatal care and nutrition. This is why the effect has slowed in recent years--these factors have been more or less maxed out. However in places where those factors have not been maxed out such as the developing world, the Flynn effect continues and in some places is even accelerating.
2) It masks a more general intellectual decline
There are many environmental factors in the modern world which have the opposite effect, and when the Flynn effect ends these factors will precipitate a crash. One of these is the modern welfare state--subsidizing the unskilled and incompetent artificially boosts birthrates among that population, which puts downward pressure on cognitive ability. Another factor is progressive culture which views childbearing as low-class and an example of women "giving up on their potential." This pushes down birthrates generally among women, and especially among intelligent women, which also puts downward pressure on cognitive ability. Finally the most profound IQ-shredding effect is from technology itself. The basic mechanism is that technology benefits those who lack natural abilities (not just cognitive) in greater proportion than it benefits those with naturally high cognitive abilities--e.g. the smartphone has increased the man on the street's range of intellectual possibilities far more than it has the scientist or the history professor's (analogously, think of how a gun benefits the physically weak more than it does the strong). This also puts a downward pressure on cognitive ability by (a) favouring the weak, and (b) facilitating dependency which causes natural abilities to atrophy with disuse.
It does not make a great deal of sense to retard those members of society who are most responsible for advancing the society's material needs. If the best solution to racial tension is basically to dumb down society, is this not a good indication of the failure of multiculturalism?