From my experience it's a lot easier to learn another language than to learn a new model of operation or new concepts entirely. And if you'll want to work with Godot, that will likely be the main barrier, and the main thing that will not be transferable to other contexts. The language however, can only make working with the concepts easier or harder. Godot team has decided that having their own language designed for dealing with the concepts of the engine makes it easier to use and results in less work than trying to adapt some existing language to the concepts of the engine. I've dealt with this a couple times, where a language was transformed so much by the context it was used in, it felt like an entirely different language.