Hey there,
Thanks for the suggestion! Right now MailChimp’s “Default Merge Tag Values” support pre-filling input fields on your plugin’s sign up form. However, the plugin does not currently provide the ability to add HTML5 placeholders. It’s something that’s definitely been discussed, and I’d be happy to pass along your feedback to the resources available on my end.
In the mean time, I’d recommend checking out an older thread that some of the forum members put together with some awesome suggestions of how to implement those HTML5 placeholders into the current version of the plugin:
http://wordpress.org/support/topic/plugin-mailchimp-list-subscribe-form-request-add-placeholder-text-for-mailchimp-widget?replies=21
If you have any questions, just let me know!
-tk
