We have in mind that username can be a lot of things including email, a unique username or even a phone number.
It depends on the approach but definitely under consideration in order to improve. Thanks!
Users only need to remember their own phone number - you send a temporary activation code via SMS to register - as painless a signup as you can get
Meanwhile it sets a higher bar than an email address for fakes signups; as a developer you have a higher degree of confidence that most of your signups correspond to a real person, which can help reduce abuse etc.
