I suggest you learn more about JavaScript, including its origin, its growth, its limitations, and its strengths, then do the same for several other languages.
if you do this, you will either see JS as the cancer it is, or you will lie to yourself and say you have "won" this discussion.
JavaScript has succeeded only because web browsers have carried it. it doesn't have enough merit to exist on its own, especially if you measure that by the JavaScript that existed early on. that was rubbish (though much simpler rubbish than today's variants) and if it weren't for the parasitic nature of JavaScript it would have died when it should have died. now, because it has been around so long and sees so much use, people believe it is a valid choice for other things. it really isn't.
TermKit is an excellent set of ideas to try to push further, but there's so much friction to just getting started with it, just trying it out. where-as the rwgular terminal is just there, single process, on our systems.
as for growability, community adoption, there are more hurdles. js isnt one thing. it's a vast vast sea of libraries & tools. even if termkit does show promise, so many js developers wont quitw understand or enjoy the particular tool/library choices made. TermKit is just before React, node.js is still quite new; it's just as JS started really settling, but barely. it's hard to imagine it would have been an ideal, modernly hackable form of js.
i still think dis-unity is a strength, that it's good that we're exploring widely, that we havent fully settled & let ossification set in. but it does mean new radical ideas have much smaller communities to support them.