Current Covid-19 Growth Rate Seems Unsustainable

In practical terms virtually all exponential functions are logistic functions:

https://en.wikipedia.org/wiki/Logistic_function

As the curve reaches the full size of the population it slows down. However, logistic and exponential functions are the same until they get close to the population bound. It's not unreasonable to believe this projection will be accurate until COVID-19 infections get close to 1B people in early May, unless significant quarantine procedures are put in place.

If quarantine procedures are enacted, you usually get "waves" of infection, where the infection spreads exponentially for a while until quarantine or social distancing is enacted, then dies out, then is reintroduced again, and this continues until all susceptible individuals have developed immunity. The point of the quarantine is not to prevent people from getting the disease (they're going to anyway); it's to lower and stagger the peak so that it doesn't overwhelm care facilities.