One of the things that improve the Raspberry Pi is faster data storage. The SD is limited in speed and can be corrupted easily. Being able to boot and run from an SSD drive over SATA would be ideal.
So, we went looking for a Raspberry Pi alternative that would have a SATA port. We found many alternatives and several have SATA ports on them. We finally settled on testing a Banana Pi M2 Berry because it is the same form factor as a Pi and therefore would fit any Raspberry Pi cases.
During our testing we discovered that we were unable to boot a standard Raspbian SD image and would need to create a separate SD image for the Banana Pi. Banana Pi requires special bootstrap code that is not compatible with the Raspberry Pi.
For this reason we don't believe any of the alternatives to the Raspberry Pi are worth pursing at this time.
Update Aug 2019: The new Raspberry Pi 4 has USB 3.0 and SSD's can be added via a USB 3 to SATA cable. While not as simple as a SATA cable, this is a viable solution for now.