The (or one of) nightmare scenario isn't Ebola as it is hard to catch and very fatal restricting the spread. A highly infectious novel virus that has a long incubation period, can freely infect other people for a long time before symptoms reveal themselves, but also with even more severe symptoms than SARS-CoV-2 including death, could be truly devastating. The odds of that are small but sadly nowhere near zero.What would happen if the COVID death rate was double (like smallpox). What if it was like the plague, or Ebola? How would the speed to vaccine differ (I know Ebola is a virus) How would the global response differ? Just a hypothetical.
What this should have taught us is that we simply aren't prepared for a pandemic. Massive funds and planning need to be put into pandemic response planning once we start getting back to normal if not sooner.