As far as I know, the issues with the SDK 2.0 and Up Board are related to a change made by the developers in the latest release (2.10.2), which they are looking into, and that earlier SDK releases before version 2.10.2 should work with the Up Board.
As the 400 Series can work with any Intel or ARM processor and just needs a USB 3.0 port though, you have plenty of choices of single-board computer or mini PC that should work with the camera.
A few suggestions for options include:
INTEL COMPUTE STICK
This is a PC on a stick, as the name suggests. Though Intel apparently does not recommend using it with a battery, and some people experienced problems with doing so, there was a report of someone who achieved stable results with a battery powered Compute Stick.
INTEL NUC 8
Intel has a new and powerful 2018 model of its very small NUC mini-PC.
Again, battery power does not seem to be officially recommended but people have done it anyway. Google 'intel nuc battery power'. Here's an example:
NVIDIA JETSON TX2
This is a popular choice for using RealSense with robotics / drones.