Besides already proposed additions or removals for server environments, I believe FitPC2 would be a great "barebone" for basic "network gateway" environments (firewall, QoS, AV, ...) I opposition to standard servers this role doesnt require heavy storage usage besides being able to boot a basic linux image.
One feature that could be really great for this would be LAN Bypass. For those of you that might not know what this is, it joins the 2 network port under certain circunstances (power down, kernel panic, etc) This is great for networking devices working as bridges (fw, qos)
Existing OEM or barebone appliances are quite more expensive than FitPC2 thus this could become very attractive from a price point of view.
This feature would require some extra internal space but as this usage doesnt require HDD it could be spared. There are different versions too, currently the most popular is called Gen 1.5 that in essence means its activated as a Bios option but can also be controlled from software.
Other improvements could be to replace Realtek with Intels but I understand this would also increase the price
Kind regards