Let's get this out of the way now, so that we don't have a repeat of all the misinformation from the demo.

>What prevents us from getting into Sun and Moon early?
Three layers of protection.
-The games' encrypted content need to be uploaded to the CDN.
-The games' titlekey needs to be made available (this is equivalent to saying the games must be purchasable).
-The games' content lock seeds need to be made available.

>How will we know when the games are on the CDN?
Pic related. I'll get a text message when they go up, just like I get texts when any other metadata changes.

>What's a titlekey?
A titlekey is a 128-bit number, that's the key to decrypting the content on the CDN.
Titlekeys get delivered to your console when you purchase a game -- there's no way to get one otherwise.
Thus, we will not have the titlekeys before release or Nintendo making them pre-purchasable, whichever comes first.

>Nintendo made the game's prepurchasable. Why can't we decrypt them?
In addition to the normal CDN crypto, sun and moon will use a content_lock seed protection system.
In addition to the normal encryption on every 3ds game, Sun and Moon will have a 128-bit "content lock seed", used to encrypt the games.
Without this value, the games can't be decrypted, even if you've installed them via pre-purchasing.

The "small update" you download on release date for a pre-purchased game consists entirely of this 128-bit content lock seed, which gets published on release.