The ability to add a 404 page for static websites would be really nice, the default 404 page on static websites is not user-friendly at all. Wouldn’t be too difficult to implement, maybe any file named “glitch/404.html” or something like that would be considered as a 404 page.
I know 404 pages are possible in non-static websites or using something 3rd-party like cloudflare workers, but this is specifically for static websites.
The ability to make the path used to view a file in the browser different than the file path in the filesystem would also be cool. E.g. having a file myfolder/myfile.html and being able to access it with <domain>/notmyfolder/notmyfile(.html) without using something like folders.