Depending on how you define "functional", it's been on the rise for decades. It's just that the goal is a horizon, not a point. For example: Does the language support recursion? It's functional by the old standard. Does it have first-class functions? Ditto, but by a newer one. And so on. These days, it seems to be about making functional composition a major theme, often with side-effect-free styles being favored. Maybe later it'll shift further, to languages derived from Coq or Agda being the things people mean when they talk about functional programming languages.