I wonder why we haven't seen yet some more optimisation for JS. The only thing I'm aware of is the Google Closure Compiler. With everyone using TypeScript, there must be a way to use all that type information to make JS run more efficiently, or compile parts of your TypeScript code.
I adore Elixir and have made a good career around it. I'll love it until my grave.
But with that many servers I can't help but wonder if Rust wouldn't be a better choice. I don't think they'll even need 100 which, as OP pointed out, will drastically reduce their operational complexity.
Furthermore, the strong static typing would have avoided the megamorphic functions right from the start.
Yeah I agree with rust, I have some simple database fetching servers that run crypto functions as well (I.e. login) and for simpler operations they can quickly get to 100K+ requests per second on a single host