why should I focus and learn ES6 when its not supported by IE? When it eventually is I will probably need to re-learn it
There are a couple of things to understand:
we can transpile es6 into es5 using a tool like babel. So if you need IE support, you can still reap all the benefits of the new es6 features while still supporting IE using babel.
IE will slowly fade away, with Microsoft pushing for Egde (which has a chrome engine)
In a project, a decision can be made not to support IE and simply inform the user they need to upgrade there browser.
es6 is just an update, its still one language. These days, to land a job as front-end developer you will very likely need to know “both”, given you want the new feature while you also might run into a legacy project which needs to be maintained.