I am currently reading a book called Visions by Michio Kaku. It was published in 1998, so its picture of the future is a little off in places. It speaks in particular at great length of the amazing benefits that will come with the completion of the Human Genome Project, whose sequencing phase was finished in 2000.
We will, according to the book, have personal genetic sequencing done by our GP, who will then be able to tell us what diseases and ailments will plague us in old age. Forensic investigators will be able to construct identikit pictures of suspects simply from DNA samples found at crime scenes! We're still waiting for those and other benefits.
The first difficulty in realising these benefits has to be the fact that "junk DNA" is no longer considered non-functional. It makes up the vast majority of our genome (some 98%) and does not code for any proteins. It is still largely a mystery, so it will complicate any genetic studies enormously.
Secondly, the sequence of base pairs of our DNA is not even everything. There's a "meta-genetic code" in the way the DNA is folded which can cause expression or suppression of genes. You can't simply tell what a person looks like from their DNA sequence. You need to know how it was folded and expressed.
I'd say we are still a long way from understanding our own genetic composition, let alone being able to exploit it in the many ways that have been suggested over the years.
Mokalus of Borg
PS - Those promises may yet come to pass.
PPS - But it will take much longer than anyone expected, because life is complex.