I do not have data, but I do have arguments.

If the economics do not work out, why did they chose to create infrastructure and take on the burden of supporting it instead of implementing backups to the popular cloud providers, and not having that extra operational burden?

Also, iCloud gives individuals 2 terabytes of storage for $11 a month. OneDrive and Google Drive are similar. S3 is less than 3 cents/gigabyte (with extra costs for reads and writes)

I guesstimate backups will take less than 100GB per user. At Apple’s consumer pricing that is slightly over half a dollar.

So, if they buy storage at bulk and get a sufficiently high number of customers, I do not see why they couldn’t make money on $2/month.