True, but that ship has long sailed; the user@domain making people think it's an email address is with us at least for another generation.

Fact is, other nomenclatures, like @user@domain are largely still up for grabs because no other protocol/platform has captured it the way email has.

This is largely a branding thing and not a protocol issue; technically speaking a URI scheme is more accurate, but that's a branding and usability disaster.