Hi,
I believe we should do - 2. use e-mail, when login isn't available for all user selectors
The idea is that websites/projects can have different creation when to use Login field and when Email field are primary identifier for their users. In real live we can't fully predict this.
Lately we see that more and more projects require Email address as their primary identifiers for the user, but still there are some projects that use Login field too.
For this reason I believe we should:
a. use Email field when Login isn't available
b. enable "use e-mail as login" option by default now for new installations
c. add Validation for user Login field using Regular Expression (as originally described)
Make sense?
DA