> Nextjs 13.1 just added actual server-side middleware

the middleware has been available for awhile, they just added a few "advanced" features it looks like.

The problem with their middleware is that it's based on their edge runtime. Which is pretty much very basic web APIs and nothing more. Unlike Express/Koa, you do not have the full node API and cannot do things like read files from the filesystem. It's a total unnecessary clusterfuck just so Vercel can get you on their cloud services. Every single day I work with Next.js I wish I had Express and a decent router.