[JdeBP]

One can, and many people have, over the years.

Some of the more interesting ideas that people have had, in my view, have been:

* ID systems that introduce hierarchies, allowing (say) a user to create multiple sub-users (one for running the WWW browser, one for running the office suite, one for running the chat program, ...);

* proper nonce ID creation with segregation guarantees (c.f. nonce SIDs in the Windows NT world); and

* IDs that are reference counted, accessible via descriptors, passable from process to process via descriptor-passing mechanisms, and explicitly supplied in system calls for opening/creating things.