I don't think they have created every single object uniquely but several objects has different properties and to be able to separate them when changing something they are often written in separate files. So it would still require quite a lot work to put it in now when a whole act is practically complete. Especially if you want it to work in every possible scenario a player might see it logical to work. And you know us players, give us a hammer and we will eventually find a scenario where it's logical for us to be able to build a spaceship with it
I'm not saying it's a bad idea as it opens up a lot of fun and interesting ways to interact with the environment. But I also don't agree with it being worth the effort seeing as they have a LOT of other things to change first and foremost for the game to feel right imo.
