I've just convinced a large, but not global, client to move from their antiquated system to Next.js. They definitely wouldn't want to run on Vercel in prod since they're obsessed with costs.... and now I'm really concerned since this and some other "next.js in production nightmares" posts have dropped. I've only ever run smaller stuff on Vercel. Super concerned.

Any sufficiently advanced development ecosystem will be full of issues and people ready to tell you about them. Whatever the flaws, it's probably still an improvement over what it replaced in your situation.

What’s the rationale behind NextJS for this client? If you’re not using Vercel, NextJS doesn’t make much sense. Something like Astro is likely to be a much better fit.