This micro version of clique-only Facebook events is not bad. If someone builds a usable version of this that will eat into a significant portion of WhatsApp groups.

I believe if your app can just record my video, then transcribe my audio to figure out details of my plan (location, time, etc.) and then post an Instagram story with my video plus metadata in an elegant way with a poll widget, that is something I would use today.

Maybe later in product lifecycle you can add more useful features within your app. But I'd definitely start out by latching on to an existing social network.