It's no trick to make something so hard that it's impossible. It's riding the line that is interesting.
Clearly, in the direction that Malbolge is hard, it is very nearly maximally hard. A LISP interpreter of this kind is, in general, not that hard. There are some conceptual challenges to implementation, but once your brain has absorbed those, it's not hard to implement. It's generally considered to be a good student project. Many people use it as a "hello world" program when learning a new language. Yet it took a decade+ to pop up. Much harder and you're not going to get anything, ever.
Presumably, there are other directions that you could make programming hard in.
Clearly, in the direction that Malbolge is hard, it is very nearly maximally hard. A LISP interpreter of this kind is, in general, not that hard. There are some conceptual challenges to implementation, but once your brain has absorbed those, it's not hard to implement. It's generally considered to be a good student project. Many people use it as a "hello world" program when learning a new language. Yet it took a decade+ to pop up. Much harder and you're not going to get anything, ever.
Presumably, there are other directions that you could make programming hard in.