In the same boat as the OP, kinda, but for me, I feel like the interesting problems at interesting scales are not being done in Node:

- I do 100% Node.js backend work and am a technical lead.

- I did a lot of Java in college, and tiny bits of Java over the past 10 years (servlets on websphere)

- I've gone through phases of doing Go in my free time, and really like it, but jobs seem scarce

- Before JS I spent ~2 year doing Python/Django professionally. I used to do all my whiteboard questions in Python but now use JS. (I've been paid to write Perl, C, & C# in addition to the languages mentioned above.)

I've looked at Elixir, Rust, & Go but none of those languages seem to have critical mass. Do I really need to learn enterprise Java to go up market in terms of money and scale?