The ACA is before the Supreme Court. If it is struck down, pre-exisiting condition protections disappear.
COVID is the mother of all pre-exisiting conditions.
It is pervasive.
It is mostly non-symptomatic or at least not differentially symptomatic in the short run from a bunch of other fairly common diseases for large segments of the population.
It is still an unknown as to what long term effects look like.
It is an attack on multiple organs and systems.
Best case scenario is that a good percentage of the population will have COVID and be mostly healthy most of the time by the time that COVID becomes an unusual and infrequent disease as social distancing, ventilation, mask wearing and other public health measures work well enough to buy time to get most of the currently not yet infected portion of the population vaccinated with a highly effective vaccine.
Worse case scenario is that we get herd immunity between the relative inefficacy of vaccines, low vaccination rates, low social distancing, low mask utilization and continual consistent spread over the next year or two. In that scenario, two thirds or more of the country will have had COVID and some non-negligible percentage of that group will have long lasting effects of their infection.
Under current law, insurers can’t explicitly look at medical history to set rates.
If the Supreme Court overturns significant elements of the ACA, then insurers can and will look at the mother of all pre-exisiting conditions to uprate or deny coverage. Even if an insurer does not want to do so, competitors that effectively screen and select members based on medical history will de facto make the non-screening insurers pick up only the sick and likely to be sick.