PipeableStream is a Node.js stream that is piped back to a response object, instead of being returned as a response body.
It is especially noteworthy as React has recently introduced renderToPipeableStream as the preferred serverside renderer function. It is the only way to render Suspense components in SSR contexts.
As far as I’m aware, SSR React apps cannot be served on Netlify unless PipeableStream is supported.
Pardon my ignorance, but PipableStream doesn’t seem to be an API like ReadableStream. That’s just something React team decided to name the function (renderToPipeableStream). The underlying API is a Node.js Stream.
Based on my searching, Node.js Streams seem to be a Node.js specific thing. We currently aim to use and provide Web Standards, so APIs that work in browsers, Node.js, Deno, and more runtimes. You should be able to use Node.js Streams within your Functions, but I won’t expect us to add support for that as a response, at least any time soon.
As for Suspense, unless I’m mistaken, it already works (at least with Next.js) on Netlify. So maybe Stream is not a requirement?