if you got an invitation to join the product breakfast, you can follow the link and change your registration to include the breakfast. The instructions say to also go to the app to add it to your calendar… but that step is NOT the registration. it simply adds it to your calendar so you are reminded. Once the app becomes available, you can do that step.
I just checked with the events team and they say that 200 people have already successfully registered for the breakfast.
(Also, i was told that the app will now be live tomorrow).