I've realized that the nicest items on my reward list are very poorly explained. Let me explain them.
Infinite Blank will, in the future, have not just a single main world but a great many secondary ones to build and explore. Some of these, like weekly worlds and experimental-rules worlds, will be run by the Infinite Blank team itself. (That is, me, until such time as I recruit other volunteer administrators.)
Others will be run by users, like you. Private worlds will, once complete, be fully-functional, fully-customizable worlds running on Infinite Blank's servers. Their owners will be able to freely share entry codes and invite as many people as they want to explore their world, and maybe contribute too. Owners will also have full administrative control over the worlds in question, and will be able to moderate and control content however they want.
Creating this option lets Infinite Blank stick to its core philosophy while at the same time allowing others to exist. Community-exclusive worlds, competitive worlds, and worlds with arbitrary themes will all be quite possible.
As examples, someone at a college could create a collaborative world with friends or classmates, then share non-editing passwords publicly to allow other players to see their work. Someone at odds with Infinite Blank's permissive philosophy could create a world more tightly regulated for some standard quality. Someone wanting to create a themed world which requires tight regulation (like comic strip worlds) or that involves risqué content could use their private world to do so.
Public worlds are a small extension of private worlds, and will have the added plus of being publicly visible on the coming world-select screen without entering an access code. They will also be subject to a light restriction regarding content moderation, to keep the game kid-safe.
I expect user-run worlds will be a nice addition to the game. It could be a while before they're available; Kickstarter donors who've earned them will have first access, naturally. In time afterwards, I will likely make them available again for a small donation. Some time after that, they may become free. Public worlds are a much more experimental affair, so we'll see about those.
Be sure to tell me what you think. :)
Footnote: regarding private world access codes, I'm thinking entering them once will permanently add a login option to one's world-select screen. EG, an explore-only code for Jimmy's Cloud City world will add lingering option [Cloud City - explore-only] which might then be added to a favorites list.