One thing I miss over my desktop calendar is the ability to add invitees to the events.

1) Add invitees from registered users list
2) Add list of email addresses (not yet registered users) with serparator as invitee list.

If this is added I can replace my email/calendar desktop application.
Thanks.

My initial thoughts are that invites should be accepted by registered members only.   This still allows you to control / restrict the enrollments with DNN groups if you wish.

Selecting invitees from registered members list generate email invite asking person to logon and enroll.
Adding email addresses would generate email invite asking person to register and enroll.  If this is a paid event redirection occurs during enrolment but after registration.

Both methods are encouragement to enroll and enforce registration.