Supposedly, a new API function has been added, and relevant structures been updated, in a recent SteamVR dev build, to allow for viewplanes that are not simply assumed to face forwards. (...although delivered matrices could already represent the rotation, it has been said.)
That should deal with matters of the angled screens.
One would assume that probably still needs engine builds to update their dealing with OpenVR and cameras.
While single viewplane planar projection can not normally deal with larger fields of view than less than 180 degrees; Do keep in mind that the promoted 200 degrees is for both eyes together. You can subtract from that, for the FOV of each screen, and consequently its in-game camera and rendered image, the part of the total FOV that will only be seen in the other one - the remainder will be lower than 180.
The wider the FOV, the less you really want to render it all to a single uniform and unbroken plane anyway, because of how detail spreads over an ever larger amount of pixels, as the eye-to-plane angle becomes more and more oblique the farther you get out in the periphery, so that you render more and more (towards infinity) detail, out where it benefits you the least. There is certainly things FDev could do there, to optimise for things like anisotropy, foveation, and lens properties. NVidia offers a set of solutions in their VRWorks suite ("single pass stereo", "lens matched shading", etc), but maybe something less proprietary might be more desireable.
