I currently have a Dropbox Pro account that we share with the family of 4. I would like to have a separate account per family member, but I am not willing to pay for four Dropbox Pro accounts. I think there is a market for a Dropbox Family plan. My thinking is that the total space for the family is 1 TB, the size of a Pro account. You could charge a reasonable amount per additional family member. I envision that you limit the number of family members such that this will not compete with your Dropbox Business offering.