It seems I was too optimistic regarding the MIPS version of the device. The binaries for it are compiled against uClibc there which is quite different than musl that is used nowadays. All ARM devices use musl also with Devolo's firmware.
Currently I'm running into a segfault when I try to run ghn_host. I probably need to make sure there is no interference and it's loading exclusively uClibc compiled libraries as shipped with the Devolo firmware.
It will require some extra tricks to get this to fully work.