Almost there already
Google Now is quite happy to tell me when to leave the house after rifling through my emails, spotting a flight reservation, sorting any delays, and knowing how long it takes to get to the airport whilst suggesting public transport options to get me there. Having it in my calendar would make it more readily checkable, as opposed to relying on Now cards to tell me when it decides to tell me.
Yes, it's a bit creepy, but at least it's a reminder that 'my' mailbox is shared with all and sundry agencies, and I get a useful service in return. I should probably be more concerned, but am not really sure it's worth it. And it had been extremely handy recently, with then showing flight trackers, delays, etc.