If it would take a decade, then it is a broken business that should cease to exist as it is doing something illegal with the collected data. What kind of business is it?
Realistically, how hard is it to automatically grab some data from a database and export it as JSON, as well as remove data from your database pertaining to a user? With a relational database, this would be a cinch. I mention the right to access the erasure right, as I estimate these will be the most frequently called upon.