I doubt Apple would go so far as designing a low volume server processor for their datacenters. It is probably not cost effective. Apple reusing their iDevice SoCs in microservers could work though.

The A9 has PCI Express lanes for NVMe flash that could be used to add wired networking and storage while the secure boot and code signing would allow them to build a microserver that only runs their code. This arrangement would also be incredibly cost effective for them.

They would want to give their SoCs have properly protected internal data paths and the necessary logic for ECC RAM before using them in micro-servers if those chip features are not already there though. If they are, I doubt that the ECC is being used in their iDevices.