>>lblume+(OP)
then replace "v8" with "arbitrary binaries" because that's true too. embed a lisp and do whatever you like, for example. Golang, C, Rust, Dart, etc are all quite common too, and nobody would call C "sandboxed".
all self-modifying really prevents you from doing is stuff like dynamically changing your permissions. which is a broadly reasonable restriction because it'd complicate the approval UI (and the actual enforcement mechanisms) quite a bit further.