For something that you think is a de-facto standard, public suffix list seems kinda raw to me for now.
I checked it for two popular public suffixes that came to mind: 'livejournal.com' and 'substack.com'. Both weren't there.
Maybe I'm mistaken, it's not a bug and these suffixes shouldn't be included, but I can't think of the reason why.
I don't know about LiveJournal, but I don't believe you can host any interactive content on substack (without hacking substack at least). You can't sign up and host a phishing site, for instance.
User-uploaded content (which does pose a risk) is all hosted on substackcdn.com.
The PSL is more for "anyone can host anything in a subdomain of any domain on this list" rather than "this domain contains user-generated content". If you're allowing people to host raw HTML and JS then the PSL is the right place to go, but if you're just offering a user post/comment section feature, you're probably better off getting an early alert if someone has managed to breach your security and hacked your system into hosting phishing.
The public suffix list interferes with cookies. So on a service like livejournal, where you want users logged in across all subdomains, it's not an option