Mandatory volunteer contribution to maintain membership status. How would you implement?
I would probably use the CiviRules extension for this (to be found here: https://civicrm.org/extensions/civirules with documentation here: https://docs.civicrm.org/civirules/en/latest/ ) and then:


set up an activity for uploading the document
set up a CiviRule with trigger new activity, condition on activity type and status (and possibly attachment) and action tag the contact as an active member.