I too would like to see this feature in RekordBox. It's strange that this functionality is currently present with keyboard binding, but not with MIDI mapping.
Add activate Memory Cue panel to the MIDI mapper
I have a DDJ400 and want to remap a controller button to show the memory cue panel. Despite it being an option using keyboard shortcuts, it isn't an option in the the MIDI mapper. Please add it.
Long and convoluted workaround using another program and AppleScript here: https://forums.pioneerdj.com/hc/en-us/community/posts/360056240052/comments/4407748376217
We should not have to go to those lengths for something so simple.