Yeah, I'm pretty sure if you put a viewscreen in the back, the engine will try to "stretch" the picture across all the viewscreen models present, and it will result in mega-distortion, and, since the player's viewpoint is between the screens (and the engine will try to stretch a 2D image through 3D), possibly a crash.
Still, try it, perhaps if the second screen is totally out of the player's field of view (as they would be, being diametrically opposed to one another) most of the time, it'll work, though I'm not convinced.
Perhaps some script could be devised so that when you're in the observation lounge, or on the bridge looking backward while the doors are open, the viewscreen model could be hotswapped to the skybox model to envelope the nacelles? Has anyone ever explored that idea?
Worst comes to worst, you could sling a box of stars around the nacelles and the Observation Lounge windows (on closer inspection, it appears you have already done that).
Another, more constructive suggestion is that you swap out the nacelles for some higher quality nacelles from one of the newer Sovs around.
I see you have scaled the model to the stock Bridge's floor plan. This highlights how dinky the old Ebridge was, as a more properly proportioned model now makes the NPCs look like giants!
Excellent work! It's a joy to see that bridge finally done justice in BC. And the Obs lounge is simply awesome.