We are working on this but it is not in place right now and won't be for quite a few months (in terms of login our focus is on agent logins as they help drive more bookings to everyone)
One thing you can see is that each customer gets a username / password (on each customer record). That can be used for start of booking engine login - but that isn't the full login that you just described. Only real use of existing customer login is in club type situations.
Customer post booking pre travel logins are going to be great (when they eventually come) but we are going to have to work extra hard on the branding of them to ensure you can put your own style on them and make them your own