The reason i didn’t want to do it this way in my own experiment if possible was because although raising the display output fools filmic by artificially raising the value of display_white, in addition to making the gamut_check_RGB issue go away it also reduces or removes tone mapping of the high end. Simply bypassing RGB gamut check function instead allows colors to avoid the perceptual salmon looking desat without giving up the benefits of normal filmic tone mapping. This comes with risk of out of gamut colors in the high end that must be assessed manually, but in my case this was preferred to the otherwise aggressive desat.
As it’s easy for me to forget while I’m in there actually using the tools, it’s also good to keep in mind that, although they can be related, gamut clipping and histogram clipping are not the same thing. Gamut clipping can happen at individual RGB channel values well below 100%. Raising the value of display_white progressively makes the histogram clipping go away, and affects gamut clipping too because (I think…) it makes the gamut checker think that a given RGB triplet is further inside the gamut rather than near the edge.
What I have done previously with v6, which is kind of similar to what you describe, is to get filmic set the way I want it, initially ignoring the desat effect in the more brilliant colors. Then using an instance of color balance RGB with a luminance mask, I reduce the brilliance of just those “highlights” that are experiencing the desat due to gamut_check_RGB until the desat goes away. Then I add another instance of color balance RGB post-filmic with a raster mask from the previously mentioned instance of color balance RGB, and simply boost the brilliance of those same highlights by the same amount used previously to reduce their brilliance. This method retains the tone mapping benefits of filmic for everything except the areas I manually manipulated. But to me this is a hassle to do, and I wanted to avoid it if I could come up with some other way, even if as a temporary bandaid until something better is available.
However I see part of your question is about maxRGB color preservation mode. I almost never use this mode as long a I can get “no” to look good. maxRGB seems to clobber local contrast and color contrast IMO and seems to really only be good for subjects where surface details are not that important as it tends to give everything a matte look. So I think part of the issue you describe is just a property of that preservation mode. If you are trying to manage smooth color transitions or maybe doing portraits then maybe maxRGB would give better results to the other modes. I have never understood why maxRGB is the default selection, as to me it almost always gives inferior results (which admittedly is a partially subjective call on my part).