If the onboard Ethernet is not required then likely the G400-S would be a better choice. However the SODIMM form factor allows one to swap out the module for upgrades and independent testing.
Both the G400-D and G400-S specifications list 12 analog inputs available, but clearly this is not possible on the G400-D as is.
About a year ago I was following this thread closely, as “Gerhard” really requested what I was looking for, basically a hardware design guide for ChipworkX equivalent, or superset of the G400HDR. That would have battery for the RTC, SD card, two or three COM ports, on-board Ethernet, USB client and touch screen. In the end I had to go with Embedded Windows 7, the full .NET framework,PC-104 adapters and SBC, which had a few issues but did work out for a medical instrument prototype.