Thanks very much for the answers.
As for point one... Have you requested a CM3 from the RPF? I know at least one of their testers (he was testing the camera interfaces) was working with one at least 8 months ago and RPF (per Eben Upton's comments) was working with NEC for 18 months before their announcement in October. I would think that the RPF would want to help you to be ready when the CM3 launches. In any case, as soon after the CM3 is available and I can afford one (finances are in a black hole at the moment), I'll test it myself.
On point three. Fair enough, though I would point out that the datasheet for the CM3/CM3L was made public 3 months ago, so the data has been out there that long.
My use case is both pretty simple and probably kind of weird. I'm using a pair of SBCs as a server and a backup server (with a replicated database). At present, I'm using Cubieboards because they have a native SATA-II interface. The primary server has a CD burner attached (via USB ) for taking backups. Both primary and secondary server are connected through a KVM switch. They are both connected to a LAN. This is why I want three connections besides the drive interface.
I very much like the "packaging" of the SATA adapter. I could stack two of them very neatly (which helps when I take everything to the convention where I run Con Reg (see www.dundracon.comhttp://www.dundracon.com). If the USB ports were stacked two high, spacers would be easy to arrange and the magnets would hold everything together.
While I would consider the CM3 sort of adequate, the limitation being that everything is on a USB 2 connection, I look forward to the potential for a future CM to have USB 3 (which will require a board redisgn, as I understand it) and take almost full advantage of SATA III.
I have tested both the 314GB PiDrive and an SSD (using a USB 3 to SATA adapter) with an SBC (Roseapple Pi) that does have USB 3. The PiDrive runs transfer rates around 80MB/s (probably pretty close the drive limit) and an SSD runs around 125MB/s, probably limited by the A9 cores of the Roseapple Pi.
My preference would be to migrate to Raspberry Pis as the software is better and maintained and upgraded (for example, the Roseapple Pi version of Debian does not use EDID to set the screen resolution and changing resolution is a major project in and of itself). The CM3 will have the added advantage of being able to boot over the USB bus, so I could use the CM3L and not need an SD card or eMMC at all.
I can live with 3 USB ports by adding a USB Ethernet adapter (I've used one with a CM1 and the SATA Adapter), but to do the full setup, I need 3 ports and the current SATA Adapter only has 2. The SATA Adapter is very close to a fully usable board, but it's not quite there.
--W. H. Heydt