Basically.
Players who attempt to join your server who do not currently have their shader level set to low or medium will not be able to enter the server, similar to the whitelist mod. This would only work in minigames, and is for stealth gamemodes where hiding in shadows is really really important.
This would also mean that players who change their shader level to low or off to easily detect people in said shadows would be kicked, and unable to reenter less they change their shader level back to how it was.
Along with that, this would only effect minigames as stated before, which means that it would not be able to be abused for server elitism.
Someone please make this. it's the only thing stopping stealth servers.