Think public suffixes! It is long, so definitely not an edge case.

You can write a small script to look up all PSL domains and check if the www and APEX domain has the same dns records.

Our implementation (we control 15 or so) does not, have a www-subdomain for the domains. Anybody can register the www-subdomains.

It's not an edge case, it's a specific customization required to support Chrome browsers only.