What is the likelihood that insurance companies will want to use genetics to exclude benefits? Very high
And very illegal. Has been for years.
Indeed, ACA also made any exclusion of benefits for pre-existing conditions illegal just recently, mandating universal coverage instead (though in a fashion that will probably cause the law to fail unless the tax penalty is significantly raised). I think that this was going to be necessary one way or another, as simply banning exclusion on the basis of genetic testing was not a viable long-term solution.
If you ban exclusion on the basis of any kind of knowledge (including genetic testing), then it means that consumers can use that knowledge to decide whether to seek coverage, but insurers can't use that knowledge to deny coverage. That means that only people likely to be sick would sign up, and thus you get the typical health insurance death spiral.
Really the only way to avoid this is to mandate that everybody buys insurance, so that the healthy subsidize the sick (which is basically how insurance has always worked anyway). In the past it wasn't a problem because genetic testing didn't tell you anything useful. Today it isn't quite far enough along to cause problems with insurance, but some day you might be able to prick a kids toe at birth and tell their mother their anticipated life expectancy (barring accidents).
Oh, I don't know what the status of life insurance is. If it too isn't allowed to discriminate based on genetic testing then eventually that law will need to change or the industry WILL fail. Of course, that could be many years off. It should be obvious though that if individuals are allowed to know their life expectancy and insurers aren't, that there isn't any way to set a price for insurance that anybody will be able to afford. When you walk in and ask for insurance the insurer can safely assume that you're going to die soon, and they'll price their product accordingly. Of course things like accidental death only policies would still be reasonably-priced, since nobody can predict who will need them.