I reached out to a school I haven't yet heard back from and was told that the applications committee was still in the process of review due to having to adjust to new working conditions, presumably because of COVID-19. I'm sure a lot of them are in the same situation. It doesn't hurt to write to them and ask when to expect an answer.
As for accepting now and rejecting later, I'm told this is actually a common practice, albeit a little shady. You want to guarantee yourself an option if the others fall through, but if they don't, you shouldn't feel obligated to go with your initial choice when another one suits you better. Sure, it risks burning some bridges with the faculty there and sucks for those on the wait list, but I think it's completely understandable -- you've gotta do what's best for you, bottom line.
Curious to hear others' thoughts on this...