I don't see how you could actually come up with new stuff in PLT without a very heavy math background, specifically in logic. I mean it's not impossible just extremely unlikely.
New programming languages aren’t usually examples of novel advances in type theory. They’re usually just novel combinations of existing features. They’re still “bleeding edge” in the sense that they’re what the industry will be using in 20 years.
(It works for programming languages, too. Hang out in a forum for a relatively-new language like, say, Elixir, and you'll hear gossip about a lot of languages whose communities would describe Elixir as a staid legacy language, that'd never merit a mention here.)