MailChimp Sync for SharePoint now synchronizes custom fields.
This allows you to use a single list in MailChimp, segmented however you wish.
MailChimp subscriber segments are based on custom fields. An example of this might be tracking the events attended by a specific person. Your MailChimp list may have a custom field called “Event” and you can now auto-synchronize this custom field from your SharePoint list.