I think there would still be a need for "files", ie, a way to store a self-contained document format in memory that is independent from the code that is working

I think there would still be a need for "files", ie, a way to store a self-contained document format in memory that is independent from the code that is working on the data at one exact moment: to allow moving documents between computers, but also to allow updating the software in a safe way (ie without losing data), to save older version of a document, but most importantly IMHO to be able to create snapshots that can be safely reloaded in case of a system crash. We're not ready to have systems that can't be rebooted.