Importantly, you can share activities with others whether or not they have Shoelace. You won't necessarily have to create a Facebook event to rope people in, then.
Don't expect to try Shoelace for a while. It's invitation-only at present, and then only in New York City for now. Whether or not it goes public will likely depend on its early performance. If nothing else, it's a relatively fresh take for a Google-made social network -- it's trying to get you off your phone instead of keeping you hooked.