You write that you currently work full time at Microsoft, a company with a large developer tools division that actively develops several language compilers. Have you reached out to managers in those groups to learn if they have (or could create) opportunities that match your interests?
If you are open to working with grammars & parsing algorithms also in non- deterministic ways, you could consider a research career in NLP.
Finally, you could apply to work for a specialist compiler company (JetBrains, Green Hills Software etc.).