As all assets are flowing in via workfront ,I feel expiration too should be handled in wkft as below :-
a) Create a dashboard for workfront users in kjft - "My assets (assets uplaoded by me) expiring in 30 days or 90 days based on e ofxpiry date Dashboard will contain metadata details of assets including expiry date.
b)Create a dashboard for "Group that uploader of asset belongs to " to show assets expiring in <=15 days
c)Create a dashboard for "asset manager/admins " to show assets expiring in <=7 days
Also schedule email notification via workfront.
Users should be able to update expiry date in wkft through these dashboards and trigger a workflow if required for review approval or send to AEM directly post update.