I never got notified of this reply 😭 I agree there could be a walled garden setup like you outline, ideal for all kinds of private groups wanting to use nostr like you would private Telegram groups (and replace them, eventually). The URL or qr code invite would be crucial in onboarding members to the group too. Right now, our local group has a main private Telegram group chat whose entry is protected from entry by a lobby chat, where people are basically asked to tell us how they found the group, and we can invite them (or not) to the main group.