The 200nit semi HDR tonecurve was created by just reworking the SegmentedSplineParams_c9 section of ACESlib.Tonescales.ctl by eye.
We went through a similar process when we were developing a 250nit ODT for using HP Dreamcolor displays with the backlight maxed out. Just running two side by side, one at 100nits using the standard transform, the other at 250 with the custom one, and tuned till we got something like felt similar in character to the stock transform, but with an additional stop and a half of additional headroom.
To tune the Vive ODT, we recallibrated one of the Dreamcolors to match the primaires, whitepoint, gamma, and brightness of the Vive.
We did that dev work using my Pure Nuke RRT/ODT implementation:
Which lets you tweak it in more or less real time. Then we copy those values back into the CTL so it we can rebuild/rebake our OCIO config from it.
The primaries and white point were given to us by Valve, but you could get them by profiling the headset directly too.