Each calendar has its own d tag, so i guess creating new npubs is more for whether you want to follow calendars of an individual, or those prepared by an org where key ownership may be passed along?
This would replace the need to the calendar kind entierly. Calendars will just be the pubkeys that create the events. Seems like a more straitforward way to delegate roles since selective premissions can be given to the calendar pubkey via a bunker