>What prevents us from getting into Sword and Shield early?
Three layers of protection.
-The game content needs to be uploaded to the CDN.
-The game content needs to be owned by an account.
-The game titlekey needs to be made available (this is equivalent to saying the games must be released).
>What's a titlekey?
A titlekey is a 128-bit number, used to decrypt content that has been downloaded from the CDN.
Titlekeys are stored in Tickets, which your console receives once a title it has been purchased has been released.
>What does "needs to be owned by an account" mean?
Starting in system version 9.0.0, Nintendo has enforced serverside anti-piracy techniques on the CDN. Downloading a game now requires authenticating with the server with a Nintendo account that owns what's being downloaded.
This means that the game content cannot be downloaded until an account can own the games -- effectively, they cannot be downloaded until they are pre-purchasable.
>Nintendo made the games prepurchasable. Why can't we decrypt them? Your Sun/Moon FAQ says titlekeys are available on purchase, and I purchased the games!
On the 3ds, this would have been true -- purchasing a game on the 3ds always gives you its titlekey. To solve the preload problem there, Nintendo introduced "content lock seeds" -- data that is unavailable until release.
On the Switch, titlekeys work the way content lock seeds did on the 3ds. They are unavailable until release (instead of a ticket, your console gets a "PrePurchaseRecord" which does not have a titlekey in it).
Without the titlekey, the games can't be decrypted, even if you've installed them via pre-purchasing. Nintendo is not stupid, and has not and will not release this value to anyone prior to release.
>What does all this mean?
-The games will probably be uploaded to the CDN in the next couple of weeks, as we approach their release date.
-The games will not be downloadable from the CDN until they can be pre-purchased, which will probably happen sometime in early November according to the Japanese Member Club.
-The downloaded games will be protected by a 128-bit value, which nobody can brute-force before the universe dies.