In Version 2.3 MailChimp Subscription option now added into WordPress Simple Registration Plugin. Now Users can be subscribed to Mailchimp Lists during Signup into defined by Admin. You don’t need any extra plugin. Admin have two option to control subscription:
Allow users to subscribe himself
This option will render All MailChimp Account Lists just about the Signup button. And user can choose lists.
Automatically MailChimp Subscription
This option will subscribe user without showing any list on Signup form. These lists can be defined by admin from settings.
Admin can also see Users status about MailChimp Subscription like shown below: