I do have to note that it was never meant to integrate the back-end into WP. The integration that is provided is only for the front end... displaying the calendar in WP.
If you want something that uses WP's user database, and permissions, then you're always going to be better off with a full-blown WP calendar.
I also have to note that I have no say in the calendar's direction, so I really can't tell you if this would ever be available - not until I get my hands on V7, which would be at the same time as you.
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