I think it's weird to suggest that programming languages are under-investigated, and the discussion he gives of it makes me question his conclusions about other fields. There are vastly different paradigms completely orthogonal to the hierarchy in that image the author uses. I don't think getting people to stop using assembly/C/fortran/cobol/php/whatever is a research problem.
I was talking to professor Shriram Krishnamurthi a week ago about a block-based, educational ML dialect I was making, and he told me that he believed that once a language had a type system as sophisticated as mine, its target audience should be using text, not blocks. So, perhaps Scratch-style languages are a dead-end, or infeasible beyond a certain level.
My personal hope for the "next level" of programming languages is those that use typed holes to interactively help the programmer construct the program.