This simple sandbox module supplies a block to allow a user to subscribe to any freeform list using checkboxes. If you use the same merge fields on different lists, the fields will be displayed only once. It also modifies the sign-up forms displayed on
mailchimp/subscribe to use the new form. It doesn't currently support interest groups, but that could be added if there's any interest (haha!).
As well as using the block, you can programatically use the form
mclisthelper_user_subscribe_form which takes an array of list entities and the user account as arguments.
This functionality belongs in the MailChimp project imho, so it will never be promoted. See #1232744: Provide one block with a drop down or check boxes for lists for progress.
- MailChimp Lists (a submodule of the MailChimp project)