TRADE BETWEEN DISTINCT SHARING ECONOMIES
Despite the enormous advantages of being in a very large sharing economy (which may over time persuade everybody on the planet to form one single sharing economy) it may happen that distinct sharing economies form. People in one region may mutually decide to share among themselves but choose not to share freely with people in another region, even though the people in that other region share freely among themselves. There may thus be distinct sharing economies, of varying sizes. What will the economic relation between them be?
Though it is impossible to predict what people will do in the future, it is possible to imagine what are some of the things they might do that are consistent with egalitarian principles in this case.
Certainly the two sharing economies from two different regions could trade with each other. Delegates from each sharing economy could meet to craft proposals for trade that, if agreed to by enough local assemblies in each region to carry out the proposal, would be carried out. For example an agreed amount of lumber would be provided by one region to the other in exchange, say, for an agreed amount of rice or whatever. The sharing economy receiving the lumber would decide democratically what to do with it the same way they decide what to do with any other resource. Ditto for the rice.
Creativity would be called upon, no doubt. What if people in one region wanted to vacation in the other region? Here's how it might happen. The delegates crafting proposals for trade might include a proposal that one region (region A) will provide two-week memberships in their sharing economy to X number of people from the other region (region B) in exchange for something (whatever is agreed upon.) Then region B democratically decides how to select the X people who will get these two-week memberships and they will enjoy a totally free two week vacation in region A.
Additionally, individuals in each sharing economy can trade whatever they have with individuals in the other sharing economy, which is barter. True, barter is problematic, which is why the people in these distinct sharing economies would be better off forming one big sharing economy for all of them. But it's their call.
What could not happen is people using money to buy and sell things with people in another sharing economy. There is no money. The reason there is no money is that egalitarians know what the use of money leads to: class inequality and related evils, as discussed here.