One of the Civet devs here. To me, the main benefit of Civet is the ability to rapidly add useful features to the language, while preserving all the benefits of TS (tooling, etc.). We're constantly coming up with ideas — from TC39 proposals, other languages, or general brainstorming — and implementing them quickly. For example, we recently added pattern matching when catching exceptions, which took just a couple of hours of development; or Python-style from ... import ... for better autocompletion of imports. All of these features are optional; you can write well-formed TypeScript as usual, and just choose to use the features you think are worth the learning curve for readers. The plugins for VSCode, Vite, esbuild, Webpack, eslint, etc. aren't perfect, but they let Civet code enjoy most of the tooling out there.

I personally use Civet for all my coding projects, as I'm devoted to it continuing to flourish. But if you ever don't like what Civet is offering you, you can eject at any time by replacing your code with the TypeScript compilation, which we make as close as we can to your input.

What happens if a TC39 proposal is rejected? That's actually the good case for us, because it means we can keep the feature as is. Civet already transpiles all features to TypeScript, so they can live here forever if we think they're good. The trickier part is when Java/TypeScript changes in a way that's incompatible with Civet. Then we plan to change Civet to match Java/TypeScript, so that we don't diverge (though compiler flags allow us to also support the older form with explicit opt-in if we think it's worth doing so).

JavaScript and TypeScript move slow. Largely that's a good thing; they're a stable foundation, and we don't want to mess them up. But it's also exciting to be on the bleeding edge, explore new ideas, and obtain new features as quickly as we can design them, instead of waiting a decade. Many features are also too niche / add to much complexity for the general JavaScript language, but they're still fair game for languages that transpile to JavaScript. See also the recent JS0 vs. JSSugar discussion.