Backup my iPhones and iPads to my NAS

I have six iPhones and four iPads in use in the house with a total of 3TB of onboard storage. I want these to all back up to the 144TB NAS storage system which is configured to synchronize to offsite storage. I obviously do not want to keep copies of any of the files on any of the PCs or MACs in the house, all of which are configured with a 4TB SSD for local use.

When is Apple going to support this rather obvious requirement?

All it would take is the ability to specify the location of the storage location in Apple Devices. Sure, I can futz about in the Registry or put symbolic links in the file store to redirect but that isn't the approach I expect from an Apple product.