As far as I understand, DX11 may indeed risk breaking mod compatibility, at least if it was ported properly so that shaders etc. were updated as well. I wouldn't oppose of mod updating though, most people only drive ISI content anyways. It's not a big sacrifice for the added benefit. The other option would be keep DX9 and implement VR as in LFS. From what I heard, this VR implementation in LFS only took a couple of weeks to code. Maybe it's not perfect, but if it works with Oculus Rift CV1 as well (not sure about that) ISI should seriously consider it. If it's really only a few weeks of work, there is nothing to lose in trialing it.