Anyway, I'm sure this will be said elsewhere in the thread but it bears repeating — the Next team similarly works hard to make sure that your Next apps can be self-hosted and run on other platforms.
While Vercel's intentions are good, and your personal intentions are beyond reproach, this strategy all but ensures eventual vendor lock-in without explicitly saying so. Vercel's compatibility will increase over time and other vendors will have best-effort implementations of certain features, but never the complete feature matrix. The industry (esp. medium/large companies) will quickly pick on the relation of "Vercel is needed for ease of mind when using SvelteKit in production", as I've heard from many companies considering/using Next.js. Do people use Next.js without Vercel? Yes. Do companies evaluating Next.js consider it vendor-locked? If they're experienced, yes.