We've seen Calendar Federation in 8.5 be very popular. Now, how about Inbox federation. Allow me to federate other people's inboxes with mine (subject to the usual access restrictions), so that I can see and action mail items in the other mailbox right from mine. I can see that being useful for
- team mail-in databases; so that I can watch them from my inbox
- personal and admin assistants can keep track of the boss or other team members that they act for
- covering absent colleagues
And you probably have more suggestions.