I'm fairly confident I will be at Princess 2021 for my first non-Marathon Weekend runDisney event. My daughter is excited to dress me up in some manner for the race.
It will very likely sell out. And it could sell out on the first day, or even the first hour of being on sale. According to posts on the DIS from the Princess 2020 thread, it looks like the 5k and 10k sold out in 37 minutes last year. So my advice is to be prepared on June 9th the moment registration opens. And I believe from past anecdotes that even being in the registration process does not guarantee your 10k registration is confirmed. So be quick through the registration process as well. Once you submit your payment, then you should be likely good to go. If you want to familiarize yourself with what the registrations look like, then Wine and Dine goes on sale on March 10th at 10am ET.