Does 'Membership Organizations' really need to be required for a Membership Type? It's meaningless for users who only offer memberships for their own organization, and it makes Membership 'feel' like a 'Relationship,' but it's not really. (E.g., as a Relationship, I would expect to be able to search for all Contacts who are 'Member of' a given organization, regardless of Membership type. I don't think this search option exists?)
For most uses, it would be more intuitive to map memberships to a Group. (E.g., users expect to be able to E-mail their Members from CiviMail, which is only possible if the Members are in a group, so now we force them through the extra step of creating a Smart Group...)
Perhaps the Membership Type form could provide either option: 'Associate this type with: [ ] Organization [ ] Group'
Or at least, each Membership could have an automatic Smart Group, to resolve the CiviMail use case described above.
Another Approach would be to allow Groups to be treated as a Membership Type. Just add a third option after 'Access Control' and 'Mailing List,' and you've got the full power of CiviMember added to Group sign-up.