Thanks for the suggestion. The API to allow you to manage the invitees in bulk, and the membership list was on our backlog already, and we have gotten sufficient demand to prioritize the work ahead of some of the other ideas we had.
Until then, the workaround we have in place is to change the membership of the space to allow anyone with the URL to join, and to lock it down to invite only after you have gotten the bulk of your users in.
Thanks for your suggestions