What are the PL features that would get the most out of the human brain?

I would think that it would have to be a syntactically simple language. The human brain isn't super efficient at processing instructions in the traditional CPU sense, so it would perform better if it "compiled" into reusable bits of "code" that could be made a habit.

Not exactly a programming language feature, but it would be nice to have a scheduler implemented somehow if that's possible. You can sort of train yourself to do this, at the cost of context switching inefficiency. Context switching is really expensive for the brain in time but can be feasible if done at boundaries of "task units" and only every few seconds.

Lisp macros. Code as a data structure is a concept that the human brain would adapt to easily(and hopefully not misuse)

Declarative programming languages based on formal logic. Have a look at the Prolog programming language to get an idea.