With this patcher, couldn't you permanently change the kernel boot command line instead of modifying the value post-fs-data? The fact that post-fs-data was available too late was precisely the reason why a "live" mod of the parameter stopped working on the Pixel. Being able to modify the kernel boot command line on-device would significantly simplify the process of preparing a given device for biQuads support. I'm guessing this is what @flar2 is doing in his ElementalX Aroma installer.
I don't think so but I'm still pretty new with boot patching. This is what I got from osm0sis on the matter: https://forum.xda-developers.com/showpost.php?p=74762672&postcount=563
I ended up going with the init.rc suggesstion which is also where franco sets some other module stuff