Hey there!.
I recently made a fresh start after few years of stopping web design work,
So when I came back I keep seeing people talk about front-end JS framworks such as Vue, Angular, React and list goes one.
As an HTMl/CSS front-end developer who’s planning to make wordpress themes, Should I consider learning one of those frameworks? How would it benefit a WP theme maker while making something for Themeforest?
Thank you!
For WordPress themes - not really (or not yet). I’m afraid compatibility with plugins that do stuff on frontend will not be really good. And also, many clients will want to create child themes, but I’m pretty sure they have no idea on how to work with Angular/Vue/React.
WordPress.org guys are planning to introduce a frontend framework (https://make.wordpress.org/core/2017/05/24/javascript-chat-summary-for-may-23rd/), but I’m afraid it will be not soon.
But you may give it a try and see what happens 
That WP framework thingie sounds really interesting!
Thank you, I’ll definitely give them a shot on my free time.