Emacs tries to represent every user interface as text. Even video editing.
Plan 9 tries to use filesystem trees as APIs for all applications and OS services.
It's interesting to abstract insights gained from extreme programs, and modify them.
We can ask: if Emacs is successful using plain text as user interface, what if we use hypertext?
Or: if Plan 9 is successful in using filesystem trees as APIs, what if we use activity streams?