The real problem here is Big Sur's root snapshot system. Everything else, as far as I'm concerned, is fundamentally trivial to deal with. I've kept SIP turned off since it was introduced, and in the brief time I was using Catalina, I had a launchd job that ran at load to set the rootfs to read write. The computer was mine, and I edited plenty of system files like this.
But Big Sur makes it all much harder, because changes to the root filesystem don't take effect until you reboot. That is really, persistently annoying!
During early betas, some Macrumors users reported that if you powered off a computer at the right point during the install process, you'd end up with a version of Big Sur that didn't use a root snapshot. If there was a more consistent way to enable that, it would help a lot.
They are now using this stuff to force you to waste 2Gib on about 6 desktop wallpapers. The only user-doable solution that won't get undone at the next update seems to be to buy a new SSD with more storage to make up for it, for 2-3X the retail price of non-proprietary SSDs.
For some reason they thought the stock wallpapers needed to change with the time of day and the way they implemented it takes hundreds of megs each. Then it is locked down by this system protect stuff so you can't get rid of them.
But Big Sur makes it all much harder, because changes to the root filesystem don't take effect until you reboot. That is really, persistently annoying!
During early betas, some Macrumors users reported that if you powered off a computer at the right point during the install process, you'd end up with a version of Big Sur that didn't use a root snapshot. If there was a more consistent way to enable that, it would help a lot.