Earlier quoted context omitted.
"There's are still some big gains python could make, if python implementations were better." At this point, I would find it far easier to believe that you are underestimating the difficulty involved in what it takes to speed up Python than that there are enormous gains yet to be had in speeding up Python. I suspect JS has had more optimization effort expended overall, but Python has still had a ton of work by lots of…
Will you please share the languages you thunk are up and coming?
In the "you probably can't convince your boss yet" category I'd recommend Crystal (https://crystal-lang.org/) and Nim (https://nim-lang.org/).
Given the programming landscape and the general direction of things lately, I also bet there's a couple of serious contenders developing out there that haven't even hit HN yet.
[1]: For at least a broad class of problems. Put Go head-to-head with a problem someone would use NumPy for and Go will go down in flames in the ease-of-use and line count department. However I use Go for a lot of networks servers (not even necessarily Web servers, but network servers) and the line count for these comes out maybe 20% larger than Python, and it doesn't take much developer cognitive energy for those extra lines. I've also used Go for some command-line type apps where the line count is probably 50% over Python, but I also got some significant wins from the type system and concurrency, so, all in all there's a lot of things I can prototype with about the same mental effort in Go as I could in Python. Being able to declare interfaces that existing types conform to turns out to cover a surprising amount of those "duck-type" scripting-type cases.