Silverpop hosts our master suppression list, but only because we don't yet have a method of importing opt-outs made on the Trilogy interface. Our unsubscribe data should live somewhere very close to the CRM, perhaps maintained by a new Civi extension.

I'm not too excited to give this new table a schema, the opt-out reason for example is not calculated when using a log_civicrm based formula and just removing active emails from the pool of emails over all time. Date added to the list and date last used don't jump out as easy or helpful, either.