This means you can't pass the game around to your friends or sell it afterwards, which completely ruins the purpose of physical media imo. I mostly play PC these days so this doesn't affect me, but it's a disappointing direction for console games. At least they could've used an empty disc that has proof of ownership.
EDIT: Bethesda has confirmed that only the PC version won't include a disc. Physical versions of Xbox will include a disc. Whew.
Probably need some way to track who owns the code in a robust way. I will not say what technology might come to mind.
The word you're looking for is "database"
Why would you need that? You don't have that with physical copies either.
The physical copy already has a tangible form which probably has copy protection built in. If a code would be transferred instead of copied, it would be necessary to know who owns it.
You would have to deactivate the game in the store before you got the code out. That deactivation would also delete the game files to clean up everything.
Maybe you made a copy somewhere else, but you'd now have to crack the DRM on most games.
Only if the game doesn't have DRM it relies on you honoring the agreement.
A similar situation would be processing refunds, where GOG allows refunds up to 30 days after purchase, even if you downloaded and launched the game.
That's the way it would need to work for Steam as an example, yes.