@dansup there may be a bit of user confusion with the latter. Considering the format of providing your handle (@<username>@<domain>) is essentially one character difference. Fediverse is bad enough for onboarding that little things here may exacerbate the problem when discussing it with novice users.

I will also second what other comments are alluding to around how there other confusion and conflicts with how people typically use subdomain (e.g., www, CMS, etc).