A lot of unicode characters are blocked for domain names for this exact reason.

wouldn't you end up with the 'xn--' ascii expansion in the url window?

In Chrome, probably [1]. Other browsers don't seem to be as strict.

[1]https://www.chromium.org/developers/design-documents/idn-in-...

Hyperlink i.e http://.com How many people will double check the url bar and notice the url is actually http://www.xn--m3haa.com/? Not all of them.

:edit+seems like the three umbrella unicode symbols are not supported on hn, are they supported in e-mails?

Most modern browser will show you the unicode version.

Nowadays most modern browsers will revert to the punycode ("xn--") if there is any chance of confusion, cf. https://en.wikipedia.org/wiki/IDN_homograph_attack