You know what, you're right. I was under the assumption that there was some kind of unique identifier in the disc that would or could transfer it to a digital license. In the case of the PS4, I'm sure there must be something...bar code, some serial number on the disc. Something that could only be redeemed once.
Or maybe there isn't and I'll be getting a disc-based console.
There isn't. That was part of MS' plan last gen, unique identifiers in discs so you could install the game without needing the disc anymore, then when you trade it in (at a licensed store) your digital license would expire. Basically discs would be tied to the console they were first installed on and you would need MS to unlock them again for trading.
Nobody liked that idea so no unique identifiers in discs.