Earlier quoted context omitted.
Not quite sure what you mean by sublanguages - procedural and declarative macros perhaps? In any case I wonder about the simplicity/complexity dance. Simplification ends up with something like Lisp, in which you write DSLs that each has to be independently learned. Elixir does something similar. Some differentiation might just be a natural consequence of chasing ergonomics.
If I had to guess: Safe Rust, Unsafe Rust, proc macros, declarative macros, the attribute language, and maybe async Rust (although I'd really just consider this sugar on Safe Rust). I love Rust, but I would love to see more syntactic unification between these components. Both macro languages, in particular.
These two are the exact same language. Some features (like calling unsafe functions, or dereferencing raw pointers) are "locked" outside unsafe blocks, but syntactically and semantically they are identical. It's easy to show this: put a unsafe block around a normal "safe" block, and all that happens is an extra "this does not need to be an unsafe block" warning from the compiler.