well, lemme think...
an excellent looking 3d cockpit will probably cause more performance hit than an excellent looking 2d one, moslty because the 3d one will probably require thousands of polys.
And as far as I can see the only things that may look better in the 3d cockpit (in a comparison between excellent 2d and 3d cockpits) are inertia (like starlancer) that is as cool as irrealistic, and lighting.
On the other hand a 3D cockpit should be faster to be built than a 2d one, and it could be done by more people and in less time than the 2d one.
But even a 3D cockpit will require a lot of textures work to look halfway decent without using true materials and 10k polys, and they will have to be custom textures, wich can't be done by everyone. Actually if you are able to draw those textures you should be able to create a whole 2d cockpit too.
Personally I think that for example you, nico, should be able to create an excellent 2d cockpit (maybe mixing a render and photoshop work).
I also think that I should be able to create a good 2d cockpit, I already used photoshop to create 2d images of complex 3d objects, with good results, so I should be able to do it ....in 2 or three months, probably more.....

(not to mention that my pc will explode if I try to create an image of the size and complexity we are talking about)
I think that even if it was possible to add em, I won't start making ship specific cockpits, either 2d and 3d, since I consider em surely cool but too timewasting and not so addictive to be worth the work.
It could be interesting the possibility to make something simple as an optional cockpit for SCP, something that could be shared, I mean just the crossbars (maybe 3d) and maybe a glass effect, like if the cockpit is projected on the window, something like WC:prophecy.
I may also be interested in giving my contribute in an eventual team project to create just a couple of good cockpits that could be given to SCP, I just don't want to waste time creating on my own many different cockpits for different ships