If I want to use merge fields in an email, I would love to be able to click through the recipient list to 'test' what the merge fields will look like for each recipient. Similar to Word mail merge how you you can click through letters to see how the fields populate for each recipient.
This would be phenomenal! We just sent out an email and the merge field didn't work right on some of our list. Unfortunately, we couldn't see it until we sent the email and then it was too late to fix it. Not being able to preview merged fields has made me very wary of using them in an email. I had the same frustration and fear in Online Express.