It is important to note that you can share activities with others, whether or not they have Shoelace. You will not necessarily have to create a Facebook event to bind people, then.
Do not expect to try Shoelace for a while. It's just an invitation at this time, and then only in New York City for now. Whether it is made public or not depends on your initial performance. If nothing else, it's a relatively new take for a social network made by Google: it's trying to get you out of the phone instead of keeping you hooked.