Ben has submitted the following suggestion:
Currently there is no way to get specific purchase information into Mailchimp with your integration, meaning that we need to use Zapier as a workaround, which adds a cost per month to our operations. More importantly opens us up to potential instability by relying on a third party tool.
It would be perfect if you could add the ability to add a 'tag' to users when they sign up for a subscription or purchase a product. Then we could segment in Mailchimp based on these tags.