It "wouldn't work" on next because your getServerSideProps receives a node http.IncomingMessage, and you would have to parse all of the form data yourself, or install a dependency to do it. Then you would have to write a second endpoint in a second file to be able to respond to a JS-enabled (fetch) request. Plus you get to implement all of the progressive enhancement yourself (state tracking, preparing that fetch request, etc).
I mean, I suppose if your baseline is writing server endpoints in assembler, all of this probably does seem pretty superficial.
> Then you would have to write a second endpoint in a second file to be able to respond to a JS-enabled (fetch) request
This is only annoying if you prefer Remix's structure of putting the endpoint and the UI in the same route. To me I have no interest in making cookie cutter CRUD apps that map pages directly to API endpoints so this is useless.
I mean, I suppose if your baseline is writing server endpoints in assembler, all of this probably does seem pretty superficial.