Quite. Though that did actually work with expansions this gen. I got the four Fallout 3 and whatever the Oblivion disc-released DLCs were from LoveFilm, installed, sent back. Worked with Saints Row 3 as well, if you already had the game then instead of buying the DLC you could rent disc 2 from the GOTY, install, then play all that without the disc. Seems any DLC released on a disc that installed then used the main game would work fine without any need to keep the disc.
The ps4 will disc check disc installed games though surely? Just like many installed pc games do currently. Have they outright stated you won't need ever to use the disc once a game is installed from the disc?
Mandatory installs fine, but surely a disc check is needed?
Otherwise everyone I know can just pool their games, install once, and pass the disc on. Which is really no kind of business model.