While i do like the the idea of DSLs and they certainly do have a place, what I would love to have is to be able to enforce a strict subset of a language in a piece of code.

Where first there was discipline and hardly passed on conventions, there now would be statically enforced rule coerction.

I deeply believe that the utility of language is not in what it enables, but in what it forbids. For example Clojure and Rust have neat mechanisms to deal with mutability, where you need something extra to mutate a value. Contrast this to C where you need to go extra lenghts to make things const (ie nobody'll do it).

Is this even possible without writing your own tools?