The discussion of who should be the guarantor members has been going on as long as I remember! Some charities limit that membership to the trustees, and some do not, and I am a member and a trustee of both types of charity.
There's been discussion about it? I thought it was universally accepted that membership would be open to the community (exact definitions may be negotiable, but the basic principle is already determined - the WMF's guidelines for chapters say if possible the organisation should have a membership structure open to the community).
Yes, there has been a discussion. More than one.
Gordo