Counter to this, there’s SvelteKit, for example, which provides „adapters“ for the different platforms, eg. Netlify, Vercel and Cloudflare. I hope that’s the way we’re going to oppose this movement as a whole.
Svelte creator and Vercel employee here. Vercel does indeed invest heavily in Svelte and SvelteKit, not least by employing me and Simon Holthausen (and potentially others in future), but there's no danger of lock-in — we're just two members of a much larger core team. Governance-wise, it's an independent project, and we'd be thrilled if other companies also chose to employ core team members! You can see pull requests like https://github.com/sveltejs/kit/pull/8740 as an example of how we approach the relationship between SvelteKit and Vercel — we're adding a new feature and Vercel will be the first adapter that gets to take advantage of it, but we're careful to design the feature in a platform-agnostic way (we even @'d a Netlify engineer to make sure that they're aware of the work in case they also want to take advantage of it).
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.
First, I appreciate your response (and overall your life work - we're Svelte.js users, about 60% of our source code is in Svelte, and we have a couple of non-critical-path SvelteKit apps).
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.
The way adapters work in SvelteKit doesn't change very fast, in fact it's stable enough that community-created adapters for things like Google Cloud can keep up just with volunteer effort. I do not think what you're describing will happen.
As the Netlify engineer that Rich @'d, I can back him up on this. SvelteKit is still admirably platform agnostic. In fact I think it supported Netlify Edge Functions before it did Vercel's!