also since typescript is being ported to go and rolldown is rust, they're stuck using IPC, so they miss out on native stuff like type awareness that a pure go toolchain would get for free

it is not. lack of plugin support is sufficient to block adoptions among other things.

but it has plugin support? what kind of plugins you mean?

look at plugin api limiation here:

https://esbuild.github.io/plugins/#svelte-plugin

esbuild's plugin support is limited which is why vite had to use rollup for prod build.