Some features that come to my mind:
1. Faster SD i/o, I understand this may be limited by the AMD SoC which provides the interface. SD cards are inexpensive, and getting cheaper and faster everyday. They are being specced to record 4K/8K video which at minimum should allow from 30-90MB/s. Version 4 of the specification speaks of 156MByte/s (FD156) and even 312MByte/s (HD312) which is approaching SSD speeds. An SD card is great as an emergency boot disk in case the SSD dies and with the right speeds could do great as an inexpensive yet speedy boot drive. If bus speeds over 150MB/s are going to be available it could be great to have 2 SD card slots so we could run them in RAID 1. See https://en.wikipedia.org/wiki/Secure_Digital#Speeds and https://www.sdcard.org/consumers/choices/speed_class/index.html
2. Two USB 3.0/3.1 internal headers and some hardware (too much to expect?) support for simple RAID like 0 or 1. A lot of Intel motherboards offer this, not sure about AMD, frankly, the failover could be achieved via ZFS or software RAID just as easily. SLC USB 3 drives are inexpensive and a great way to free up the precious few SATA slots which could be freed from the burden of hosting the OS. Especially with virtualization support, we could throw VMware in RAID on 2 USB drives and use 1 SATA for the VMs and another SATA for storage. See http://www.newegg.com/Product/Product.aspx?Item=9SIA8E03G61057 or https://www.amazon.com/Mach-Xtreme-USB3-0-Drive-Write/dp/B00JE5AS4A
3. A new enclosure, please. One that can accomodate 2 SSDs or even 2 HDDs.
What do you guys think?