Calconnect is working on a draft sharing RFC at the moment - draft-pot-caldav-sharing
That has this to say:
The "ORGANIZER" iCalendar property value in the iCalendar data MUST match a calendar user address of the sharer (owner) of the shared calendar. The DAV:owner WebDAV property MUST be present on a shared calendar and MUST provide a reference to a principal-URL of the sharer (owner) of the shared calendar. Clients can use this value to determine what the allowed "ORGANIZER" iCalendar property values are. The server MUST reject any attempt by a sharee to create an iCalendar component with an "ORGANIZER" property value other than the sharer (owner) of the shared calendar.
Unless that approach changes, I think it is unlikely, although it isn't ultimately my decision. I assume the reason is because allowing multiple organizers of a shared calendar would break most peoples' model of how scheduling functions should work. i.e. Allowing this would result in problems.