The vendor let us know that there should be no required changes on our API/connector due to this upcoming change for the Mandrill product.
So from our perspective, you should be fine, but you do want to be sure to follow through on your account to be upgraded to the MailChimp add on in time.
Hope this helps
Migration went fine, but the pricing @ Mailchimp is a complete disaster, it is 4 times the price that I used to pay.
Apparently they do not really value current Mandrillapp users.
I will switch over to Sendgrid (Which I already use anyway)
Had some issues with that, but I already planned a meeting with @roshan_gonsalko to fix that.
Many thanks so far!