Hi Vera,
Very interesting question, in the scope of GDPR.
It would mean that there would be a link in the template, leading to a webApp, not only to unsubscribe partially or of all services subscription, but also set the different optin levels.
And there would be such information at contact level (nms:recipient if factory schema is used).
Then the tracking process / workflow would take into account this optin level option to manage the tracking feature accordingly. It would mean Adobe Campaign R&D team involved, this executable process that runs on MTA server can't be change by AC customers even with admin privileges.
Because in Europe we are very concern by all that kind of questions, I expect Adobe R&D would really GDPR requirements and not only PII sysfilter schema as it is the case so far.
Regards.
J-Serge