Poly or not - there are exactly two things that make it incredibly hard to get out of Gmail, and one of them is most certainly the advanced calendar sharing features. I have 13 calendars, including the ones shared with family and kids and partners. It's a lot, but it's not more than I really need.
The other one is, how does one migrate email into something imap/smpte given over a decade's worth of emails with more than one label.