Yes, this has been implemented. The onStartSaveUserRegistration trigger now includes a reference object of the user being created. It's accessible with var1. You can use that trigger to set data on the user object that isn't being set by registration. Example as follows.
Global
Triggers: onStartSaveUserRegistration
Type: Code
User: Automatic
Access: Everybody
Action
Method: PHP
Code:
$variables['var1']->set( 'email', 'bypass@example.com' );
Parameters
References: Variable 1