ASK HN: Would you be interested in a user management service?

I had this idea recently of a system to manage users of a webapp. Some of the features it would have are:

1. Ability to register/login any user via Facebook/Twitter/Google/Email.

2. Tracking usage of the webapp by each user.

3. Classification of users based on their usage history.

4. Feature gatekeeping based on user clasification.

5. Single click communication with all users irrespective of service used to signup (don't have to jump through hoops and get email ids for each user and deal with the hassle of sending email)

6. Rapport building with users by automatically sending out emails based on predetermined events/conditions.

7. Posting to the service via which the user logged in without having to deal with their APIs.

Would you be interested in using such a service for your next webapp? If so, how much would you be willing to pay per month per 1000 users for it?