Hi Marco,
I don't have a great solution for you. We were hoping something like this would never happen, but here we are
I have a few options for you, none perfect:
1. Bug Laminar Research - I'd be surprised if this gets you anywhere. Laminar Research usually does that they think is "right" and don't generally budge from it. It's a good thing in that they've faced off against giants like Microsoft since the 90s, while holding their way. The downside, as you've seen, is they may decide to change a functionality and kill off a few add-ons if they believe it provides a better path forwards technologically. If enough users bug them saying "please open upon your shaders, it killed off a few of our add-ons" they may revert. More likely though is a response like "We're sorry about that, but overall we cannot allow that to hold back our engine development."
2. Get used to X-Plane 11 Native VR - Most likely this will be your only option for X-Plane VR in the long run, if you're set on X-Plane, there really isn't much choice. They will improve performance over time hopefully, and you can always turn down settings.
3. Vote with your wallet, give FlyInside Flight Simulator a try. It's not as full featured as X-Plane, and still missing many features, but rapidly improving. If it meets your needs, it does have fantastic smooth VR with many features
4. Vote with your wallet, give Prepar3D a try. It's also a very full-featured flightsim, although different from X-Plane in how it looks and feels. You can either try their native VR (it does tend to run better than X-Plane native), or try FlyInside P3D4 (similar experience to FlyInside XP, although also tends to get higher FPS).
5. See if you can procure a copy of X-Plane 11.25, or X-Plane 10. Not really a great solution in the long-term, as there will be no updates to those products
I wish I could give you a better option, but that's the reality we're facing. Laminar, for their own reasons, closed up shaders. Unless they can be convinced to change back (unlikely), it'll be native VR only from here-on-out. Thank you for being our long-time customer, I hope that you can find a way to continue enjoying VR flight!
Thanks,
Dan