Pattern matching (and expression based assignment, of which idk if there’s a proposal for or not) are two things that would really drive a ton of value.
It's going to end up looking a lot like C# [0][1]; these two/three (JS/TS, C#) languages have been converging for a while now. Now just waiting for C# to get official first party discriminated unions!
Just an FYI for those unaware TS & C# are both creations of Anders Hejlsberg & his colleagues at Microsoft. Both are some of my favorite languages as well.
We would all benefit if JS was more like C# in my opinion.