Hi Kevin, 

This is one area that was really focused on in the latest builds. The goal was to make everything accessible at a glance, but not be too in your face or take up too much real estate. We took inspiration for the layout from some of the popular email clients that users are familiar with. And we are hesitant to put them in a dropdown because some of these messages are very important to be seen at a glance. 

However, when viewing various mailboxes, I've found that most emails won't have more than 1 or 2 messages in the email header. 

Well, this feature doesn't even work properly, so maybe you should fix that first:

Then consider underlining or putting bullets in front of the "show image" choices.  Not aware of any email clients that have sentences with hyperlinks to take actions on messages.  Most are buttons.

Also, you said you're hesitant to put things in a drop-down.  Then why are Reply All and Forward in a drop-down? Those are "very important to be seen at a glance."

Not trying to be criitical, just trying to make the product better before it's released so users won't be calling with questions on how to do things or looking to find another mail program.