We've been using Missive for a couple of weeks now and we really miss one thing — the ability to set due dates for conversations/ emails.
It would be great if you could add a due date next to a label, for example, and it would show on a message preview in the middle panel.
Thus it could be used as a tool to prioritize tasks. Also you could add filters Due today, Tomorrow, Next 7 days, Without due date.
As I understand, a lot of people use conversations as checklists for tasks. So it would be very useful both for emails and conversations.