basically using the -visual illusion- of brick physics to make it look like you get crushed by a giant brick or something
so if your brick physics are off they don't appear and you have no idea what happens
it's their loss don't force it
Exactly this. People will lose out on the illusion of a huge boulder smashing down on them without brick physics, however they still have the outcome of straight up dying. With brick physics on, you may be able to avoid the trap due to visual cues. Similarly, you could have a server dedicated to creating complex rube goldberg machines, and the server will have zero value to anyone with physics disabled.
On the other hand, shaders being less than minimum can directly affect
other players on the server, not just the ones with shaders off. For the individual enjoyment of players having shaders on or off doesn't matter... it's when players disable shaders to negatively affect the gameplay or gain an unfair advantage that it becomes a problem.
Pretty much all issues could be solved with making shaders be a serverside setting with. Perhaps 3 settings: Minimum, Maximum, Range. Minimum allows all shaders from its value and higher to join, maximum lowers higher values down to its value, and range allows all shaders between two values to be used. By default servers would be set to minimum with OFF as its value.
But then again this requires an addition to the base game to enforce its policies, and even then there will likely be workaround add-ons involved, but at the very least you have most people who are too lazy to seek out said add-on and will just work within the server's settings.