Why can't you replace the SSD?

They've started using a proprietary SATA connector.

It's not SATA, it's PCI-E, which is a lot faster.

PCIe, which is reasonably standard.

Quick, find me a replacement at an online retailer. Then tell me how reasonable it is. There is currently only one supplier and they charge a fortune.

Not to discount your point about retail availability, but this appears to use the M.2 (NGFF) format, which has been widely praised (outside of any Apple context) as an industry-standard approach to flash memory.

http://www.anandtech.com/show/6293/ngff-ssds-putting-an-end-...

The M.2 form-factor is available for both SATA and PCIe cards. PCIe versions are becoming the new normal, due to the speed increases - http://www.tested.com/tech/pcs/456464-why-ssds-are-transitio...

uhm, well OWC is always good for it: http://eshop.macsales.com/shop/SSD/OWC/

Yeah, like I said only one supplier and the cost is astronomical.