didn't know if the terrain thing is fixed with the change from DX7 to DX9, but I think making EECH compatible if it isn't supporting 3D at the moment would be a lot of work.
There are much other things to do before.
The last time I used 3D was somewhere during the late 90's with the old NVidia cards and the Elsa Revelator shutter glasses
It was a cool feature, cause it was simply integrated in the drivers, but then NVidia changed to their own extremly expensive 3D Vision, which at the end was nothing other as the shutterglasses and I lost the interest on it. The only possible solution after this was to use anaglyph glasses which wasn't a real good deal, cause of the adulterated colors.
I also own a Pimax VR, but the use of it is very limited. Even Falcon BMS doesn't support VR at the moment, so I think in EECH it's also useless (even with some workarounds to get VR running in unsupported games). Only simulators I know of supporting 3D or VR are DCS, Aerofly FS2, X-Plane and FSX/P3D with the use of Flyinside.