> So, for Nginx/Apache, are you suggesting Arc might be able to handle uploads if it's sitting behind Nginx/Apache acting as reverse proxy doing buffering?
Nope, that won't help.
> so it's better to have a separate setup of Nginx/Apache (with PHP or whichever) handling file the uploads
That's the easiest approach. Not that you'd need PHP, just pop in a module to handle file uploads for you.
> Or is it more like doing anything with big files in Arc is a no-go
Not Arc as such but the implementation in srv.arc isn't designed for large files. You could read the old MZScheme documentation at http://docs.racket-lang.org/mzscheme/index.html and figure out how to read an input stream into a binary buffer, but it would be more work.