Top down control is kind-of hard. Given increased availability of genetic data, democratised action is easier to envision. You start off with compatibility tests against genetic disorders [1]. Then those that lead to potentially the better offsprings [2]. That opens the door for egg/sperm selection [3]. Then third-party gene introductions [4]. All the way to complete designer babies. These action may even completely cut out evolution from the equation, but evolution can be sneaky.
At every step of the way it becomes slightly more acceptable to push the boundaries just so slightly.
[1] Been the case for many decades now in the case of sickle-cell anaemia, this affects partner selection. In the last decade selection against mutations in BRCA1 and BRCA2 i.e the "breast cancer genes", has lead to searches for egg donors. Also, some people with history of severe depression that runs in the family are self selecting against child bearing (this selection is more common among females).
[2] This could even be pseudo-science at the beginning.
[3] Sperm and egg banks already allow for a crude version of this.
At every step of the way it becomes slightly more acceptable to push the boundaries just so slightly.
[1] Been the case for many decades now in the case of sickle-cell anaemia, this affects partner selection. In the last decade selection against mutations in BRCA1 and BRCA2 i.e the "breast cancer genes", has lead to searches for egg donors. Also, some people with history of severe depression that runs in the family are self selecting against child bearing (this selection is more common among females).
[2] This could even be pseudo-science at the beginning.
[3] Sperm and egg banks already allow for a crude version of this.
[4] Either natural or synthetic.