Syntax is syntax, whether it's Lisp or C. What I mean is I hardly think that a new language is what GPU programming needs to break into the mainstream.

What I believe GPU programming needs is tools that people can easily add to their current environments or that they can easily extend their current algorithms with. NumbaPro, OpenACC, and Thrust allow that.

In addition, the reason it's hard to express structured data and nonuniform computation is because those aren't things GPU architecture excels at. It excels at doing uniform operations over large chunks of memory. I'm sure that Harlan is pushing the boundary of what you can do on a GPU, but it's not going to exceed the limitations imposed by the hardware.