Ability to sort your inbox, updates-page, forums-page etc. by sender.
This way you could see all the mails you received from different senders grouped together (instead of having to do a search, which only shows you the results of 1 sender).
Now your limited to the chronological hierarchy…
Which is not always the most efficient when checking unanswered emails of the last 3 weeks. :d
Maybe this is out of the scope of Right Inbox, I don’t know, but I thought I’d suggest it anyway.