One concept I've considered is each parcel having shares. Or a pool of shares that applies to any property. The group would have to make a plan for each property (how many homesites, how large is a homesite/private area), then determine how many shares one needs to claim a homesite.

There are many ways to slice things up, and I think many of them will work. What's more important than "which practical solution is best" is if all parties understand and agree to their own terms.

This is somewhat similar to the original concept of condominiums from days of old. 

 I agree. The purpose of agreements is to ensure that everyone continues to agree with each other. Terms to agree are highly specific and constantly evolving. Interdependency means agreements are explicit and consciously chosen with clear exit options. Everyone is self responsible to change dependency terms once their needs and wants change over time.