I'll second that! The ability to turn emails into Next Actions in my main system is actually the one feature that got me to switch to Oulook some years ago. It feels *much* more natural (to me at least) than having a separate "Action" repository for emails.
Yes, IMHO this is a must-have feature for a GTD system. We are very proud of how easy is turning emails into tasks in Needian - Organize in 1,2,3