share members across multiple buddypress installs

I'm thinking big....I have one main site that I'm starting with it's own buddypress goodness so that members can create their own page and share progress on music lessons, share videos/soundcloud links, etc. I want to "future-proof" the concept so that if it takes off I will have a whole community of different spinoffs, with this website being on the same hierarchy as the new ones. My question: is it better to create that parent structure now knowing that I'm only developing on that one child? I'm concerned because I want members to be apart of the parent should that time come. Or should I just develop the child only as a standalone install and in the future worry about linking members across the new idea with the existing one?