SO links require just the question ID; short enough to memorize.

Sure, but the SO link was just an example. HN does it with any link, like this one which is 1000 characters long:

https://example.com/some/path?foo=bar&baz=bat&foo=bar&baz=ba...

If the website or app has a good UX for displaying/sharing URLs, the length doesn't really matter.