I've used your plugin on multiple sites now, and really appreciate its ease of use.
However, the one issue I've found is that for MailChimp lists that use groups, the comment form checkbox doesn't automatically subscribe them to the top group. That's fine for some MailChimp lists that use either or radio boxes, for example--they'll send to the entire list when they send their main email. However, I use four different groups and never send to the whole list. Thus, my comment form subscribers are falling through the cracks because they are never getting added to any group. And manually going back through all my subscribers to make sure there aren't any group-less subscribers is a pain.
I know your group options are for your Pro plugin, but could you at least allow us to set a default group for the comment form checkbox? Thank you!