I miss a much one feature "Switch to Previous Layer". I mean analogy to behavior of keyboard shortcut “/” which is assigned to "Switch to Previous Preset". IMHO this would be very, very handy (speedup workflow and reduce distraction). I often jump between 2 layers and don't want to think which is over and which is under (it's required for using PageUp PageDown keys).
My proposal key is “;”. It’s not assigned to any action and on keyboard it’s near other shortcuts releated to switching (“/”, “,”, “.”).