It would mean that bigendian platforms will be actively maintained again, so this riddle would get solved.
Just FYI, I made an experiment and simply put Steve McCreas's "big end" read and write functions into use by disabling ALLEGRO_BIG_ENDIAN macro there. They seem to work nicely for Windows version (functions they use are actually std file routines, which are redefined for big-end case only).
I had to write my own implementations for little-endian getshort and putshort, however, but later I found they were already written in wgt2allg unit.
At the moment there are only few places where I cannot just plain "merge" Steve's code into default code, namely in compress.cpp and also in wfnfontrenderer implementation where you (or tobihan?) used psp_get_char function in little-endian version. I mean, it should certainly be possible, but I haven't tried yet.
Also in some cases there was big-end read/write functions prepared for a struct, but for some reason they weren't actually used; GameSetupStructBase struct for instance.
I guess CJ and Steve were couple of steps away from implementing endianess-independent code to the engine, but just did not finish this job.