Fair. 
The discussion quickly moved to freeze as that is usually the primitive people ask for here.
arbitrary() is compatible with what I laid out for inline asm blocks so I am confident it is compatible with the rest of the compiler. It does have the problem of leaking the contents of uninit memory into the program; that is a separate problem to the inline asm concerns. (Let's not derail this thread by talking about such leakage, we already have Rust needs a safe abstraction over uninitialized memory for that.)