I have a PhD in programming languages; and I hire people with these backgrounds (compilers, PL, verification, synthesis). As others have said, if you've looked at LLVM, I'd find that interesting, but for practical use, there are more useful + interesting + fun things out there.

E.g. SMT solvers (CVC, Z3, or the like) -- infinitely more fun; and require experience to truly understand what works and what doesn't. Or if you've done something really novel with meta-programming or designed a custom DSL for a domain.