In reality, the burden of implementing this new system falls on the developer and not on Apple.
Technically the only thing that Apple MUST do in order to comply with this is to update the TOS that 3rd-party payment services are no longer forbidden.
Then any new submissions after Dec 9 will allow links to outside systems.
This ruling does NOT mean that 3rd party systems are allowed (accepting CC payment within the App). The ruling only requires that a link to Safari is provided moving them outside the app for the transaction. Of course the link could include unique identifiers for the individual user and that could affect user privacy and link tracking.
Ultimately this means that a developer could completely bypass the In-App system and unlock features with credit cards on their website... giving the developer 97% of the purchase price instead of 70%/85%. Another advantage is immediate payment instead of waiting 30+ days for Apple to payout. The disadvantage is that users will have to go through a whole lot of additional steps instead of the one-click purchase that In-App provides... so even though the developers are making more per transaction, they might actually be making less overall because of the increased user difficulty in purchasing.
Apple did announce that App submissions will be reviewed in Dec, but slower than normal. If Apple really wanted to be a pain they could rescind that announcement and start the holiday on Dec 9 but not allowing any of those submissions to go live until Jan ? when they come back.
The one added wrinkle being that it seems that it would be ok if Apple takes a cut of the 97% purchase price for itself (presumably after the fact via some sort of periodic reporting requirement).