Apps could simulate cities like massively-multiplayer online (MMO) games sharded player populations. You can "move" from one shard to another, but you leave your connections behind.

If we could stratify the app, we could observe whether different shards have their own "personality" or culture, or how "immigration" is affected by influencers (or not).

What was once a load-balancing scheme for performance becomes a way to observe common algorithms across different contexts.

You'd have to somehow segment links though. A link takes you back out to the Internet, so we may find homogenization or flattening as the same links are shared among shards.

One solution is only in-app links work, and only within the shard.

Basically, any features to enforce "physical separation" that enables cities to grow "on their own."