Theres one big but.. on MorphOS or AmigaOS 3d-mouse isn't supported, and working without one these days is hopeless. Its just essential in 3d modelling.
It's not quite as bad as you make it sound. I have tried Space Navigator USB
(which I believe to be nowadays among the most popular models, at least it's cheap) and it's a standard HID device, you can see the values for all 6 axis (and both buttons) in Poseidon.
Of course any implementation for using that would be MUCH more clean if MorphOS supported joystick units with >2 analog axis, but hey, at least there shouldn't be any low level reverse engineering needed.
As for "legacy units" (like the serial model you mentioned), that would probably take more effort to support. And considering a supported (although more restricted) brand new unit is iirc well under 100 euros...
As for the project, sounds interesting and I have quite a bit of OpenGL experience, but I don't think my current job contract would allow participating in this...
[ Edited by Jupp3 On 2012/3/22 13:24 ]