Since ED hasn't chimed in all these years, I'm guessing with how the engine handles the HUD and HMD overlay, that it's not possible or would take more work to happen than what more important tasks ED is working on need.
The resolution of VR, even the Pimax Crystal, just isn't the same as three screens at 4K each since a part of the image in VR headsets is stereoscopic overlap. When I can get the equivalent of horizontal 11,520 pixels, with 190 degree total FOV, with 120 degree stereopsis FOV and perfected passthrough for cockpits, then I'll ditch my triple screens. Until then, I'll use triple screen or quintuple screen possibly in the future. Since that's likely a more niche setup than VR users, I'm suspecting we'll never see the HUD and HMD overlay system overhauled for triple screen.
Just the limited features of triple screen in the sim so far says it's a side thing added with no real tuning features from within the game. Look at RF2, RaceRoom, AMS 2 and ACC triple screen support. They all have various features to calculate each screen's size, position (distance, horizontal and vertical) and/or angle relative to the user's eye line. I seriously don't understand why all PC games, like ARMA series, DCS World and many other first person based games don't have triple screen support or proper support. That was always the draw of PC gaming, that it was doing things that consoles wouldn't. Hopefully we can see some development on better multiscreen support in the future. But, I'm not counting on it. Especially with video card price hikes possibly ending the PC games golden age.