But I can see it being useful in the niche area of someone who needs to do server side rendering for performance (every millisecond to first render counts), while keeping the code simple by not having a second technology to do that rendering, and they need the same thing to be a SPA. Maybe a GMAIL type application? And again the user has to care - I don't care if I wait 10 seconds for my mail app to load as I'll be spending minutes in there once it does, and you've locked me in for other reasons anyway.
This might matter for SEO but to be honest you could just have a non-JS version of the same page which looks different for SEO purposes.
Next.js seems pretty hot, so I am probably missing something :-).
I'd rather not use JS on the server myself, so for my projects I'd either make a SPA with API backend and no server side rendering. Or just a classic "rails style" crud app with a sprinkle of JQuery.
I hope someone chimes in and tell me what I am missing and why to use Next.js other than "I only want to do JS and React for all the things."