Definitely an interesting question!
Interactive email is an exciting topic, and one we’re working hard to help push! However, there are still a lot of reasons to use Email on Acid.
A huge one when it comes to Interactive Email is fallbacks. Many developers are coding interactive email with varying states. As Rebelmail say in this blog post: http://blog.rebelmail.com/email-client-support/ they see email in 3 states; interactive, limited and static. It’s easy when coding out a crazy cool interactive email to forget about the email basics and those static and limited clients. That’s when we come to the rescue, we’re on hand to make sure your lovely interactive quiz still does the job in Outlook 2003.
I’d be interested to hear your thoughts on the future of email and email testing too!