But does the working-set cap _work_? In that scenario where you've got heavy memory pressure I still think it doesn't.
If the background process is typically touching less than 32 MiB in a second then a per-second trimming could reduce the working-set effectively.
If the background process is typically touching more than 32 MiB in a second then the fault-time trimming doesn't work because while it trims the memory from the working set, there is no time for the memory to be paged out, and if the memory did get paged out it would make it even worse because it would need to be paged in. So, CPU (and perhaps disk) overhead is increased, but memory pressure remains the same.
The problem (a process touching too much memory) is real. However the solution does not work. A working-set cap doesn't actually reduce memory pressure on foreground applications any more than a per-second trim.