It'd be awesome if other there could be integration with other Hosted Exchange providers besides Office 365.

Even if it means the user enters credentials beyond UN/PW to include Exchange domain and/or server URL, it'd make the "business class" email/contact/calendar integration full complete as you'll have all the major players: Google, Microsoft O365, and Exchange-only providers (or providers, like us, who have separate Hosted-Exchange but also offers Office Apps powered by Office 365, which effectively emulates an Office 365 experience, if not surpasses it).