Subdomains are part of the URI authority component so they should be shown. It will look like `something.github.io` or whatever.
This list is necessary anyway, because you have top level domains that look like .co.uk, so you can't just split the domain name by dots and take the last component to determine the top level domain.
So, not saying I unconditionally like the fact they are hiding important information in the URL bar, but I would not say their default behavior is that broken.
[1] https://publicsuffix.org - probably the list being mentioned in the video linked by the parent commenter, I guess