@kuddel : we are not that far away! I managed to load up the client, it already shows the splash with shader and simulation object loading progress, but as soon as the first clbkUpdate is sent in Orbiter's EndTimeStep() function, a null-ref exception gets thrown. I think I know why: due to my naive approach, I've disabled the DX7 mouse/keyboard/joystick interfaces, which gives their corresponding internal objects null-refs. During the clbkUpdate, D3D9Client certainly will directly or indirectly try to get those input objects, which return null.
Unfortunately, I can't debug the GFX client here, perhaps a quick uncomment of core calls in the clbkUpdate could make it run, even if it won't be responsive to controls at first. I've updated the ZIP with my current workspace content:
https://snoopie.at/face/beta/x64-Debug.zip
Note that I've removed the Texture folder redirect in the config file, because for some reason the GFX client seems to ignore it, at least it searches for the necessary textures like e.g. Null.dds in the base folder instead of the redirected one. I've therefore copied those textures into my workspace, so the client boots up initially (until the null-ref exception, that is).
It is already coming together, exciting!
Edit: some picture to tease it a bit: