They could potentially release source only with no art assets. Then you wouldn’t be able to compile the game without either owning the game or pirating the assets elsewhere. But it would allow community members to update the game when it breaks or to add new features. Similar to the Mario 64 decompile.

While all this would be great for consumers it would probably take legislation to get publishers on board with something like this. Publishers have a financial incentive to let the games languish then force you to pay to get a “remastered” version.