You are basically taking on customer data archiving as a part of your business. If you are doing this as a business, everything has a cost and that cost should be passed to the customers.

There is a reason that companies doing long term record retention charge absurd amounts for it.... Iron Mountain takes on a ton of liability and responsibility to keep your crap intact while they have it. I would never take that on willingly.

Some people I know offer to package and transfer the assets to the customer as a paid service when the project is done, making long term storage their problem. (Photo, design)

I also have friends who do the contract line that assets are only kept for a year.

Truthfully... As a business, why would you want to keep anything? If the customers lose their data they need to pay you to make thing again which is better for you.