Sharing the UI thread with logic is something to be mitigated when building UIs, it's not a feature.

In theory, maybe. In practice, your UI thread very rarely has to do the kind of heavy lifting that would block it so badly you actually have problems.

I have encountered this -- for example parsing very large incoming JSON payloads -- but very rarely. And if you really need to mitigate it, there are webworkers.

There's... a large number of languages with both of those features.

Could you name few better than js?

In the context of writing reliable software for a spacecraft? Pretty much anything with a reasonable type system, for a start. Maybe C#, or some reasonable subset of C++20, or Rust. Maybe Reason or OCaml.

I mean very clearly the good people at SpaceX have heard of these languages and decided against it. I think JS and Chromium are the best UI kit I can think of in terms of man hours to get X done. If you're careful the only thing I've ever had issues with is latency, but in space if you're in a situation where missing a frame or two is important you're already beyond fucked.

From my experience, Qt/QML is way better for things like that. I mean, the UI does not need to be responsive, does it?

Maybe they couldn't afford the Qt license.

Many people are using TypeScript these days, it works very well.

I like C# and Rust too. I've built UI's in C++ and MFC/OpenGL/DirectX. It remains my fairly strong opinion that JavaScript is well suited to UI development.