But PEPs are not enforced in the language level. Also there are cases where there could fit two simple expression in a lambda. Also the language still doesn't stop you from abusing lambdas, you can nest them. It could be stated in one of the PEPs that "no overly complicated lambdas" and that's it, there is no need for the language to enforce this.

PEPs are literally the language, in my opinion. It may not be enforced on an implementation level, but some have been. You can't mix spaces and tabs now. That seems like a style choice being enforced on every level.